Aqueous polymerization of perfluoromonomer using hydrocarbon surfactant

ABSTRACT

A process is provided for the polymerization of fluoromonomer to an dispersion of fluoropolymer particles in an aqueous medium in a polymerization reactor, by (a) providing the aqueous medium in the reactor, (b) adding the fluoromonomer to the reactor, (c) adding initiator to the aqueous medium, the combination of steps (b) and (c) being carried out essentially free of hydrocarbon-containing surfactant and resulting in the kickoff of the polymerization of the fluoromonomer, and (d) metering hydrocarbon-containing surfactant into the aqueous medium after the kickoff of polymerization, e.g. after the concentration of the fluoropolymer in the aqueous medium is at least 0.6 wt %, the metering being at a rate reducing the telogenic activity of said surfactant while maintaining surface activity.

FIELD OF THE INVENTION

This invention relates to the use of hydrocarbon surfactant as thestabilizing surfactant in the aqueous dispersion polymerization offluoromonomer.

BACKGROUND OF THE INVENTION

In the interest in replacing ammonium perfluorooctanoate as thestabilizing surfactant in the polymerization of certain fluoromonomers,notably VF₂, recent patents disclose the use of hydrocarbon surfactantsfor this purpose. For example, U.S. Pat. No. 7,122,610 (Wille et al.)demonstrates the use of certain alkane-sulfonates, sulfones, anddisulfones in the polymerization to form non-elastomeric fluoropolymerscontaining at least 71 wt % vinylidene fluoride (VF₂). Such polymers areknown to be low melting, i.e. polyvinylidene fluoride (PVDF) has amelting temperature of 155-192° C. (p. 27 of S. Ebnesajjad,Fluoroplastics, Vol. 2 melt Processible Fluoropolymers, Plastics DesignLibrary (2003)). U.S. Pat. No. 7,521,513 (Tang) demonstrates the use ofsodium octyl sulfonate in the polymerization to form VF₂/HFPfluoroelastomer, wherein the low molecular weight of the fluoroelastomeris indicated by its inherent viscosity being determined by the MooneyViscometer method, wherein the fluoroelastomer is flowable at 121° C. sothat its resistance to shear can be measured at this temperature. U.S.Pat. No. 3,391,099 (Punderson) demonstrates in Example VI the use ofsodium lauryl sulfate in the polymerization of TFE and a small amount ofHFP to form a sinterable modified PTFE. Example VI also uses 260 ppm offluorinated surfactant, AFC (ammonium ω-hydrohexadecafluoronanoate), sothis polymerization is not fluorosurfactant-free.

There is a need for greatly reducing or entirely eliminatingfluorosurfactant in the aqueous dispersion polymerization offluoromonomer to form fluoropolymers, e.g. the non-melt-processibleperfluoroplastics such as, polytetrafluoroethylene (PTFE) and themelt-fabricable perfluoroplastics such astetrafluoroethylene/hexafluoropropylene copolymer (FEP) andtetrafluoroethylene/perfluoro(alkyl vinyl ether) (PFA).

SUMMARY OF THE INVENTION

The present invention satisfies this need by the process forpolymerizing fluoromonomer to form a dispersion of fluoropolymerparticles in an aqueous medium in a polymerization reactor, comprising(a) providing the aqueous medium in the reactor, (b) adding thefluoromonomer to the reactor, (c) adding polymerization initiator to theaqueous medium, thereby kicking off the polymerizing of thefluoromonomer, and (d) metering hydrocarbon-containing surfactant intothe aqueous medium after the kickoff of the polymerization, wherein theaqueous medium is essentially free of surfactant before the kicking offof the polymerizing of the fluoromonomer and no halogen-containingsurfactant is added to the aqueous medium during or after the kickingoff of the polymerization. With respect to steps (b) and (c), theaddition of initiator and fluoromonomer in these steps may be conductedin reverse order, but the stepwise sequence of (b) and then (c) ispreferred. This is Process 1. All the preferences disclosed hereinaftercan be used in the practice of Process 1.

Preferably, the metering (d) is at a rate reducing the telogenicactivity of the hydrocarbon-containing surfactant while maintainingsurface activity to stabilize the dispersion of fluoropolymer particlesin the medium during the polymerizing. Preferably, the metering of thehydrocarbon-containing surfactant into the aqueous medium is commencedwhen the concentration of fluoropolymer as particles in the aqueousmedium is at least 0.6 wt %. The polymerization of the fluoromonomer iscontinued to completion after the kickoff and during the metering ofstep (d), optionally with the step of adding more initiator to theaqueous medium, if necessary for the continuation of the polymerization.

This polymerization process can be practiced with all its preferencesdescribed above and hereinafter also preferably additionally providespolymerization sites dispersed in the aqueous medium prior to thekickoff of the polymerizing of the fluoromonomer.

The polymerization process of the present invention may alternatively bedescribed as Process 2. Processes 1 and 2 are the same invention, butdescribed differently. Process 2 can be described as follows:

A process for polymerizing fluoromonomer to form a dispersion offluoropolymer particles in an aqueous medium in a polymerizationreactor, comprising an initial period and a stabilization period,wherein

the initial period comprises

preparing an initial dispersion of fluoropolymer particles in an aqueousmedium in the polymerization reactor and

the stabilization period comprises

polymerizing fluoromonomer in the polymerization reactor, and:

adding hydrocarbon-containing surfactant to the polymerization reactor,

wherein during the stabilization period no fluorosurfactant is added.The initial period of the polymerization process preferably includes theproviding of polymerization sites prior to kicking off of thepolymerization reaction as described for Process 1. In the stabilizationperiod, adding hydrocarbon-containing surfactant is preferablyaccomplished by metering of the hydrocarbon-containing surfactant intothe aqueous medium as in Process 1. The result of the polymerizing ofthe fluoromonomer in the stabilization period forms the dispersion offluoropolymer particles resulting from the polymerization process. Thestabilization period is the period during which the fluoropolymerparticles of the initial dispersion of fluoropolymer particles grow insize by precipitation of the polymerizing fluoromonomer to form thelarger, final particles of the final dispersion of fluoropolymerparticles.

Some of the preferences for Process 2 include the following,individually and in combination:

Preferably, the initial dispersion of fluoropolymer particles isessentially free of fluorosurfactant.

Preferably, during the stabilization period no halogen-containingsurfactant is added.

In one embodiment of the invention, the preparing of an initialdispersion of fluoropolymer particles comprises adding to thepolymerization reactor:

(a) aqueous medium,

(b) water-soluble hydrocarbon-containing compound,

(c) degradation agent,

(d) fluoromonomer, and

(e) polymerization initiator,

wherein the degradation agent is added prior to the polymerizationinitiator. This embodiment of the invention operates to providepolymerization sites prior to kicking off of the polymerization reactionas described for Process 1. Preferably, the water-solublehydrocarbon-containing compound is added in an amount of 50 ppm or lessthan 50 ppm. Preferably, degradation agent is added in an amountsufficient to obtain an aqueous medium essentially free of thewater-soluble hydrocarbon-containing compound. Preferably, thewater-soluble hydrocarbon-containing compound is selected from cationicsurfactants, nonionic surfactants, and anionic surfactants. Preferably,the water-soluble hydrocarbon-containing compound is ethoxy-containingsurfactant. Preferably, the polymerization reactor is essentially freeof water-soluble hydrocarbon-containing compound in the initial periodafter the preparation of the initial dispersion. Preferably, thedegradation agent is a compound which is the same as or different fromthe polymerization initiator. Preferably, polymerization of thefluoromonomer in the reactor causes polymerization kick-off and thepolymerization reactor is essentially free of water-solublehydrocarbon-containing compound at the kick-off.

Preferably, the hydrocarbon-containing surfactant is metered into thepolymerization reactor during the stabilization period, preferably at arate sufficient to reduce the telogenic activity of thehydrocarbon-containing surfactant.

Preferably, the adding of the hydrocarbon-containing surfactantcommences when the concentration of the fluoropolymer particles in theaqueous medium is at least 0.6 wt %.

Preferably, the hydrocarbon-containing surfactant is anionic.

Preferably, the hydrocarbon-containing surfactant is hydrocarbonsurfactant.

Preferably, the hydrocarbon-containing surfactant is a compound of theformula R-L-M wherein R is an alkyl group containing from 6 to 17 carbonatoms. L is selected from the group consisting of —ArSO₃ ⁻, —SO₃ ⁻,—SO₄—, —PO₃ ⁻ and —OOO⁻, wherein Ar is an aryl group, and M is aunivalent cation, preferably selected from H⁺, Na⁺, K⁺ and NH₄ ⁺.

Preferably, the polymerizing is carried out in the presence ofpolymerization initiator.

Preferably, the process further comprises passivating thehydrocarbon-containing surfactant, preferably by reacting thehydrocarbon-containing surfactant with an oxidizing agent. Preferredoxidizing agents are hydrogen peroxide or polymerization initiator.Preferably, the passivation of the hydrocarbon-containing surfactant iscarried out in the presence of a passivation adjuvant, preferably ametal in the form of metal ion. Preferred metals have multiple positivevalences. Most preferred passivation adjuvants are ferrous ion orcuprous ion. Preferred embodiments of the invention passivate thehydrocarbon-containing surfactant prior to, during, or after theaddition to the polymerization reactor.

Preferred fluoromonomers are selected from tetrafluoroethylene (TFE),hexafluoropropylene (HFP), perfluoro-2,2-dimethyl-1,3-dioxole (PDD),perfluoro-2-methylene-4-methyl-1,3-dioxolane (PMD), perfluoro(alkylvinyl ether) (PAVE) and mixtures thereof, preferably tetrafluoroethylene(TFE).

In a preferred process during the stabilization period, the amount ofthe hydrocarbon-containing surfactant added into the reactor iseffective to provide the dispersion of fluoropolymer particles having asolids content of 45 wt % or greater than 45 wt %. Preferably, toachieve this solids content, the amount of the hydrocarbon-containingsurfactant added into the reactor is 3000 ppm or greater than 3000 ppmbased on the weight of the fluoropolymer particles.

Preferably, the fluoropolymer particles are fluoroplastic, preferablyperfluoroplastic.

In accordance with another embodiment of the invention, preparing theinitial dispersion of fluoropolymer particles in the aqueous medium inthe polymerization reactor is carried out by adding apreviously-prepared fluoropolymer dispersion to the aqueous medium.Additional embodiments of the invention include a fluoropolymerdispersion obtainable by the process according to any one of thepreceding claims and a fluoropolymer resin obtainable by isolation fromthe fluoropolymer dispersion. Preferably, the fluoropolymer dispersionand/or resin is selected from the group consisting of PTFE, andmelt-fabricable copolymer comprising 40-98 wt % tetrafluoroethyleneunits and 1-60 wt % of at least one other monomer and wherein themelt-fabricable copolymer is preferably a copolymer containing greaterthan 75 wt % perhalomonomer, preferably tetrafluoroethylene.

These preferences listed above for Process 2 can also be usedindividually or in any combination in the practice of Process 1. Thedisclosure hereinafter applies to Processes 1 and 2 and variationsthereof.

The hydrocarbon-containing surfactant metered into the aqueouspolymerization medium (Process 1) and added to the reactor (Process 2)is the stabilizing surfactant for the dispersion of fluoropolymer,fluoroplastic, or perfluoroplastic, particles formed during thepolymerization. In addition to the C—H bonds present in thehydrocarbon-containing surfactant, the carbon atoms of the surfactantcan be substituted with other elements, notably halogen such as chlorineor fluorine. Preferably, the monovalent substituents, as elements of thePeriodic Table, on the carbon atoms of the surfactant are at least 75%substituted with hydrogen, more preferably at least 85% and even morepreferably, at least 95%. Most preferred, the hydrocarbon-containingsurfactant is hydrocarbon surfactant, which means that the carbon atomspresent in the surfactant that could be substituted by monovalent atomssuch as halogen, such as fluorine or chlorine, are instead substitutedby hydrogen, whereby the hydrocarbon surfactant is free of such halogensas fluorine and chlorine. Accordingly, in hydrocarbon surfactant, 100%of the monovalent substituents, as elements from the Periodic Table, onthe carbon atoms of the surfactant are hydrogen.

The telogenic activity of the hydrocarbon-containing surfactant, orsimply its telogenicity, is primarily the result of reaction between thehydrocarbon-containing surfactant and radicals in the polymerizationsystem. In effect, the result of telogenicity is inhibition of thepolymerization reaction. There are many pathways which manifesttelogenicity, but regardless of the pathway, telogenic behavior is thebehavior which leads to a reduced number of growing polymer chains andthereby a reduced rate of polymer production and/or a significantreduction in polymer molecular weight.

The aqueous medium being essentially free of surfactant prior to kickingoff of the polymerization reaction (Process 1) and during the initialperiod after preparation of the initial dispersion of fluoropolymerparticles (preferred form of Process 2 in which the polymerizationreactor is essentially free of water-soluble hydrocarbon-containingcompound) includes the essential freedom when the surfactant ishydrocarbon-containing surfactant, such as hydrocarbon surfactant, andhalogen-containing surfactant such as fluorosurfactants. Thus, inaccordance with this aspect of the invention, the aqueous medium is alsoessentially free of C—H bonds present in the hydrocarbon moiety of anyof the surfactants or hydrocarbon-containing compound, particularly thehydrocarbon-containing surfactants. The aqueous polymerization mediumbeing essentially free of the hydrocarbon-containing surfactant meansthat any amount of such surfactant that is present in the aqueous mediumat the time of polymerization kickoff will not detrimentally inhibit thepolymerization reaction, neither its kickoff nor the polymerizationreaction occurring after kickoff. Thus, the delayed addition of thehydrocarbon-containing surfactant after polymerization kickoff describedin Process 1 and the addition of this surfactant in the stabilizationperiod described in Process 2 is the first addition of a stabilizingamount of surfactant for the dispersion of fluoropolymer, includingfluoroplastic, particles growing during the polymerization reaction inthe stabilization period.

While the hydrocarbon-containing surfactant contains C—H bonds, it canalso contain other monovalent substituents on the carbon atoms, such ashalogen atoms such as chlorine or fluorine, thereby becominghalogen-containing surfactants. When the predominant halogen substituentis fluorine, the resultant surfactant will be referred to asfluorosurfactant Typically, in the halogen-containing surfactants, thecarbon atoms of the surfactant that are substituted with monovalentelements are primarily substituted, e.g. at least 70%, with such halogenatoms, most often fluorine. With the presence of halogen atoms in suchsurfactant, it may be desirable to undertake a process for removing orrecovering or disposal of the surfactant from the aqueous polymerizationmedium after completion of the polymerization to satisfy cost andenvironmental concerns. One reason for minimizing halogen-containingsurfactant from the aqueous medium is to save removal (from the aqueousmedium) and recovery cost. Even then, complete removal or disposal isvery expensive. Preferably, therefore, the aqueous polymerization mediumis also essentially free of halogen-containing surfactant. This appliesto the aqueous medium prior to kickoff as described in Process 1,whereby the aqueous medium is essentially free of all surfactant, and tothe initial period of the polymerization as described in Process 2.Thus, if any halogen-containing surfactant, including fluorosurfactant,is present in the aqueous medium within the reactor beforepolymerization kick off, such amount is insufficient to form thestabilizing function of the dispersion of fluoropolymer, includingfluoroplastic, particles formed after such kick off and in thestabilization period described in Process 2. Refraining from adding anyhalogen-containing surfactant to the aqueous medium in the reactoreither prior to, during or after polymerization kickoff described inProcess 1 and during both the initial period and the stabilizationperiod described in Process 2 is most preferred, eliminating the needfor removal and recovery.

The present invention as a variation of Process 1 can also be describedas a process for polymerizing fluoromonomer to form a dispersion offluoropolymer, preferably fluoroplastic, more preferablyperfluoroplastic, particles in an aqueous medium in a polymerizationreactor, comprising kicking off the polymerizing of the fluoromonomer byadding polymerization initiator to the aqueous medium, the medium beingessentially free of surfactant at the time of the kicking off, andmetering hydrocarbon-containing surfactant, preferably hydrocarbonsurfactant, into the aqueous medium after the kickoff of thepolymerization, the metering being at a rate reducing the telogenicactivity of the hydrocarbon-containing surfactant while maintainingsurface activity to stabilize the dispersion of fluoropolymer particlesin the medium during the polymerizing. The polymerization of thefluoromonomer can be continued to completion after the kickoff andduring the metering of the hydrocarbon-containing surfactant into theaqueous medium, optionally with the step of adding more initiator to theaqueous medium, if necessary for the continuation of the polymerization.Preferably, no halogen-containing surfactant is present in or added tothe aqueous medium at any time during the polymerization reaction inthis variation of Process 1 and in Processes 1 and 2. The preferencesdisclosed hereinafter also apply to this embodiment of thepolymerization process.

A preferred embodiment of the process of the present invention is theadditional step of passivating the hydrocarbon-containing surfactant,preferably hydrocarbon surfactant, that is used in step (d) of Process 1and in the stabilization period of Process 2. Passivation of thestabilizing surfactant reduces the telogenicity of the surfactant so asto reduce the time of polymerization to a given solids content afterkickoff. The passivating is preferably carried out by oxidizing thesurfactant such as by reacting it with an oxidizing agent preferably inthe presence of a passivation adjuvant as will be described hereinafter.

With respect to the preferred additional step of providingpolymerization sites dispersed in the aqueous medium prior to thekickoff of the polymerizing of the fluoromonomer in Process 1, thisadditional step is also preferably included in the practice of theinitial period described in Process 2. These polymerization sites serveas nucleation sites for the precipitation of fluoropolymer,fluoroplastic, or perfluoroplastic, as the case may be, onto therebygrowing dispersed particles during polymerization, resulting in thefluoropolymer particles in the final dispersion of fluoropolymerparticles being smaller in size than if such polymerization sites werenot present. The polymerization sites can come from a variety ofsources. For example, they can come from fluorine-containing polymer,such as made by seed polymerization in the presence of surfactant toobtain the fluorine-containing polymer as dispersed particles in theaqueous medium in which they are formed. Such surfactant can be ahalogen-containing surfactant such as fluorosurfactant, wherein themonovalent substituents on carbon atoms of the surfactant are primarilyfluorine. Only a small amount of halogen-containing surfactant isnecessary to maintain this dispersion, compared to the amount ofhydrocarbon-containing surfactant used to stabilize the dispersion offluoropolymer particles resulting from the polymerization step. Thisreduces the amount of halogen-containing surfactant for removal orrecovery, if desired, from the aqueous medium.

Alternatively, the dispersion of polymerization sites can behydrocarbon-containing sites, preferably hydrocarbon sites. Thecombination of hydrocarbon stabilizing surfactant and hydrocarbonpolymerization sites provides a polymerization system that is free ofhalogen-containing surfactant, eliminating any need forhalogen-containing surfactant.

Another surprising result of the present invention is the capability ofthe polymerization process, Process 1 or Process 2, preferably includingpreferred embodiments, to achieve a very high solids content ofdispersed fluoropolymer particles. Preferably, solids contents of are 45wt % and greater than 45 wt %. The process therefore provides for suchhigh solids dispersions, especially PTFE dispersions, which arestabilized by hydrocarbon-containing surfactant, and which are obtaineddirectly by polymerization as disclosed in Example 10, not requiring aseparate concentration step.

DETAILED DESCRIPTION OF THE INVENTION

Fluoromonomer/Fluoropolymer

The fluoromonomers are the monomers that polymerize or copolymerize toproduce fluoropolymers, preferably fluoroplastics. Fluoropolymers,including fluoroplastics, preferably contain at least 35 wt % fluorine,based on the total weight of the polymer. The disclosure hereinafter isapplied primarily to the polymerization to make fluoropolymers, but thisdisclosure is also applicable to making fluoroplastics, as well. Whenhydrogen is present in the fluoropolymer, the amount of hydrogen ispreferably 5 wt % or less, based on the total weight of thefluoropolymer. The preferred fluoroplastics are perfluoroplastics, whichare polymers in which the monovalent substituents on the carbon atomsforming the chain or backbone of the polymer are fluorine atoms, withthe exception of comonomer, end groups, or pendant groups from thepolymer backbone. Preferably, the comonomer, end group, or pendant groupstructure will impart no more than a total of 2 wt % C—H moiety, morepreferably no greater than 1 wt % of C—H moiety, with respect to thetotal weight of the perfluoroplastic. Preferably, the hydrogen content,if any, of the perfluoroplastic is no greater than 0.2 wt %, based onthe total weight of the perfluoroplastic. The perfluoroplastics areobtained from polymerizing perfluoromonomer.

The preferred fluoropolymers are the fluoropolymers that most oftenexhibit a melting temperature and possess crystallinity such that theyare not fluoroelastomers. Such fluoropolymers typically havingcrystallinity and melt temperature characteristics are referred to asfluoroplastics, including perfluoroplastics. Preferred fluoroplasticsand perfluoroplastics have sufficient crystallinity that they have aheat of fusion by differential scanning calorimetry (DSC) of at least 9J/gm as determined according to ASTM D-4591 or, if amorphous, such asTFE/PDD copolymer, have a glass transition temperature of 50° C. orgreater. Additional distinction from fluoroelastomers is that thepreferred fluoroplastics and perfluoroplastics do not exhibit thefluoroelastomer characteristic of glass transition temperature below 25°C. In addition, fluoroplastics and perfluoroplastics do not possess thecombination of low flex modulus, high elongation, and aftercrosslinking, rapid recovery from deformation. One significance of thisfact is that fluoroplastics made by the present invention include veryhigh molecular weight polymers such as polytetrafluoroethylene (PTFE),much higher than that of fluoroelastomers, which obtain their strengthfrom being crosslinked. Such PTFE has a molecular weight (Mn) of atleast 1,000,000, usually well in excess of that amount, e.g. at least2,000,000, as compared to much lower molecular weights offluoroelastomers (uncrosslinked). Fluoroelastomers have a Mn that is asmall fraction of the PTFE Mn and gain their dimensional integrity bycrosslinking, whereby it is satisfactory if the polymerization processmakes a lower molecular weight polymer, i.e. the presence of telogenicactivity in the aqueous polymerization medium is more tolerable to makefluoroelastomer than fluoroplastic. The use of hydrocarbon-containingsurfactants, including hydrocarbon surfactants, in the process of thepresent invention would be expected to prevent the high molecularweights of fluoroplastics from being obtained. Notwithstanding thisexpectation, high molecular weight fluoroplastics, notably PTFE, areobtained by the process of the present invention.

In greater detail, the preferred fluoromonomer used in the process ofthis invention is preferably perfluoromonomer independently selectedfrom the group consisting of tetrafluoroethylene (TFE),hexafluoropropylene (HFP), perfluoro-2,2-dimethyl-1,3-dioxole (PDD),perfluoro-2-methylene-4-methyl-1,3-dioxolane (PMD), perfluoro(vinylether) and perfluoro(butenyl vinyl ether) and mixtures thereof.Preferred perfluoro(vinyl ethers) include perfluoro(alkyl vinyl ether)monomers (PAVE), wherein the alkyl group contains 1 to 5 carbon atoms,such as perfluoro(propyl vinyl ether) (PPVE), perfluoro(ethyl vinylether) (PEVE), and perfluoro(methyl vinyl ether) (PMVE) and mixturesthereof.

Perfluorovinyl ethers also include those useful for introducingfunctionality into fluoropolymers, preferably fluoroplastics, mostpreferably perfluoroplastics. These includeCF₂═CF—(O—CF₂CFR_(f))_(a)—O—CF₂CFR′_(f)SO₂F, wherein R_(f) and R′_(f)are independently selected from F or a perfluorinated alkyl group having1 to 10 carbon atoms, a=0, 1 or 2. Polymers of this type are disclosedin U.S. Pat. No. 3,282,875 (CF₂═CF—O—CF₂CF(CF₃)—O—CF₂CF₂SO₂F,perfluoro(3,6-dioxa-4-methyl-7-octenesulfonyl fluoride)), and in U.S.Pat. Nos. 4,358,545 and 4,940,525 (CF₂═CF—O—CF₂CF₂SO₂F). Another exampleis CF₂═CF—O—CF₂—CF(CF₃)—O—CF₂CF₂CO₂CH₃, methyl ester ofperfluoro(4,7-dioxa-5-methyl-8-nonenecarboxylic acid), disclosed in U.S.Pat. No. 4,552,631. Similar fluorovinyl ethers with functionality ofnitrile, cyanate, carbamate, and phosphonic acid are disclosed in U.S.Pat. Nos. 5,637,748; 6,300,445; and 6,177,196.

The invention is especially useful for polymerizing when producingpolytetrafluoroethylene (PTFE) perfluoroplastic including modified PTFEto produce dispersions thereof in an aqueous medium.

Polytetrafluoroethylene (PTFE) refers to (a) the polymerizedtetrafluoroethylene by itself without any significant comonomer present,i.e. homopolymer, and (b) modified PTFE, which is a copolymer of TFEwith such small concentrations of comonomer that the melting point ofthe resultant polymer is not substantially reduced below that of PTFE.The modified PTFE contains a small amount of comonomer modifier whichreduces crystallinity to improve processing, examples of such monomersbeing such as perfluoroolefin, notably hexafluoropropylene (HFP) orperfluoro(butyl)ethylene, and perfluoro(alkyl vinyl ether) (PAVE), wherethe alkyl group contains 1 to 5 carbon atoms, with perfluoro(ethyl vinylether) (PEVE) and perfluoro(propyl vinyl ether) (PPVE) being preferred.The concentration of such comonomer is preferably less than 1 wt %, morepreferably less than 0.5 wt %, based on the total weight of the TFE andcomonomer present in the PTFE. A minimum amount of at least about 0.05wt % is preferably used to have significant effect. PTFE (and modifiedPTFE) typically has a melt creep viscosity of at least about 1×10⁶ Pa·sand preferably at least 1×10⁸ Pa·s and, with such high melt viscosity,the polymer does not flow in the molten state and therefore is not amelt-processible polymer (fluoroplastic). The measurement of melt creepviscosity is disclosed in col. 4 of U.S. Pat. No. 7,763,680. The highmelt viscosity of PTFE arises from its extremely high molecular weight(Mn), e.g. at least 10⁶. PTFE can also be characterized by its highmelting temperature, of at least 330° C. (1^(st) heating), usually atleast 331° C. and most often of at least 332° C. (all 1^(st) heat). Thenon-melt flowability of the PTFE, arising from its extremely high meltviscosity, manifests itself as a no melt flow condition when melt flowrate (MFR) is measured in accordance with ASTM D 1238 at 372° C. andusing a 5 kg. weight. This no melt flow condition is an MFR of 0. Thehigh melt viscosity of the PTFE reduces the ability of the molten PTFEto reform the “as polymerized” crystal structure upon cooling from thefirst heating. As a result, this high melt viscosity leads to a muchlower heat of fusion obtained for the second heat (e.g. up to 55 J/g) ascompared to the first heat (e.g. at least 75 J/g) to melt the PTFE,representing a heat of fusion difference of at least 20 J/g. The highmelt viscosity of PTFE enables its standard specific gravity (SSG) to bemeasured as a characterization of extremely high molecular weight. TheSSG measurement procedure (ASTM D 4895, also described in U.S. Pat. No.4,036,802) includes sintering of the SSG sample free standing (withoutcontainment) above its melting temperature without change in dimensionof the SSG sample. The SSG sample does not flow during the sintering.

The process of the present invention is also useful in polymerizing lowmolecular weight PTFE perfluoroplastic, which is commonly known as PTFEmicropowder, so as to distinguish from the PTFE described above. Themolecular weight of PTFE micropowder is low relative to PTFE, i.e. themolecular weight (Mn) of the PTFE micropowder is generally in the rangeof 10⁴ to 10⁵. The result of this lower molecular weight of PTFEmicropowder is that it has fluidity in the molten state, in contrast toPTFE which is not melt flowable. PTFE has melt flowability, which can becharacterized by a melt flow rate (MFR) of at least 0.01 g/10 min,preferably at least 0.1 g/10 min and more preferably at least 5 g/10min, and still more preferably at least 10 g/10 min., as measured inaccordance with ASTM D 1238, at 372° C. using a 5 kg weight on themolten polymer.

While the low molecular weight of PTFE micropowder imparts meltflowability to the polymer, the PTFE micropowder by itself is not meltfabricable, i.e. an article molded from the melt of PTFE micropowder isuseless, by virtue of extreme brittleness. Because of its low molecularweight (relative to non-melt-flowable PTFE), it has no strength. Anextruded filament of PTFE micropowder is so brittle that it breaks uponflexing. Generally, compression molded plaques cannot be made fortensile or flex testing of the PTFE micropowder used in the presentinvention, because the plaques crack or crumble when removed from thecompression mold, whereby neither the tensile property nor MIT Flex Lifecan be tested. In effect, this polymer has no (0) tensile strength andan MIT Flex Life of zero cycles. In contrast, PTFE is flexible, ratherthan brittle, as indicated e.g. by an the MIT flex life (ASTM D-2176,using an 8 mil (0.21 mm) thick compression molded film) of at least 1000cycles, preferably at least 2000 cycles.

The invention is also useful for producing dispersions ofmelt-processible fluoroplastics, including perfluoroplastics, that arealso melt-fabricable. Melt-processible means that the fluoroplastic canbe processed in the molten state, i.e., fabricated from the melt usingconventional processing equipment such as extruders and injectionmolding machines, into useful shaped articles such as films, fibers, andtubes. Melt-fabricable means that the resultant fabricated articlesexhibit sufficient strength and toughness to be useful for theirintended purpose after the processing in the molten state. Thissufficient strength may be characterized by the fluoroplastic by itselfexhibiting an MIT Flex Life of at least 1000 cycles, preferably at least2000 cycles, measured as described above. The strength of thefluoroplastic is indicated by it not being brittle. The fluoroplasticsdescribed hereinafter are melt processible and melt fabricable unlessotherwise indicated.

Examples of such melt-processible fluoropolymers, preferablyfluoroplastics, most preferably perfluoroplastics, include homopolymerssuch as polychlorotrifluoroethylene and polyvinylidene fluoride (PVDF)and copolymers of tetrafluoroethylene (TFE) and at least oneperfluorinated copolymerizable monomer (comonomer) present in thepolymer usually in sufficient amount to reduce the melting point of thecopolymer substantially below that of PTFE, e.g., a melting temperatureno greater than 315° C.

A melt-processible TFE copolymer typically incorporates an amount ofcomonomer into the copolymer in order to provide a copolymer which has amelt flow rate (MFR) of 0.1 to 200 g/10 min as measured according toASTM D-1238 using a 5 kg weight on the molten polymer and the melttemperature which is standard for the specific copolymer. MFR willpreferably range from 1 to 100 g/10 min, most preferably about 1 toabout 50 g/10 min.

A preferred melt-processible copolymer for use in the practice of thepresent invention comprises at least 40-99 mol %, preferably 60-99 mol %tetrafluoroethylene units and 1-60 mol %, preferably 1-40 mol % of atleast one other monomer, to total 100 mol %. Preferred comonomers withTFE to form perfluoroplastics are perfluoroolefin having 3 to 8 carbonatoms, such as hexafluoropropylene (HFP), and/or perfluoro(alkyl vinylether) (PAVE) in which the linear or branched alkyl group contains 1 to5 carbon atoms. Preferred PAVE monomers are those in which the alkylgroup contains 1, 2, 3 or 4 carbon atoms, and the copolymer can be madeusing several PAVE monomers. Preferred TFE copolymers include FEP(TFE/HFP copolymer), PFA (TFE/PAVE copolymer), TFE/HFP/PAVE wherein PAVEis PEVE and/or PPVE, and MFA (TFE/PMVE/PAVE wherein the alkyl group ofPAVE has at least two carbon atoms). The standard conditions for MFRdetermination under ASTM D 1238 for FEP and PFA are the use of a 5 kgweight on the molten polymer in the plastometer and a melt temperatureof 372° C. within the plastometer.

The present invention is also applicable to polymerizing fluoromonomerthat provides —CH₂— recurring groups in the polymer chain, along withperhalocarbon recurring groups preferably TFE and/or HFP, wherein theresultant polymer is a fluoroplastic, not fluoroelastomer. Preferablythe hydrogen content of the fluoroplastic is 5 wt % or less, based onthe total weight of the fluoroplastic. An example of such afluoroplastic is TFE/vinylidene fluoride-based copolymer, wherein theamount of VF₂ and other monomers incorporated into the TFE copolymer isinsufficient to impart fluoroelastomer characteristics to the copolymer(see Example 11). Preferred fluoroplastics comprise 25 wt % VF₂ or less,more preferably, 20 wt % or less, even more preferably 15 wt % or less.

Preferred fluoroplastics are the perfluoroplastics selected from thegroup consisting of PTFE, and the melt-fabricable copolymers mentionedabove comprising 60-98 wt % tetrafluoroethylene units and 2-40 wt % ofat least one other perfluoromonomer. Another group of preferredfluoroplastics are those in which the polymer chain is composed ofgreater than 75 wt % perhalomonomer units, preferably TFE, HFP, andmixtures thereof, preferably at least 78 wt % of such recurring units,more preferably at least 80 wt % of such recurring units, and mostpreferably at least 85 wt % of such units. TFE is the preferredhalocarbon recurring unit. The remaining recurring units, to total 100wt % of the copolymer, can be selected from C—H containing comonomer orhalocarbon comonomer, preferably perfluoroolefins such as HFP and PAVEmonomers described above.

The Polymerization Process

The polymerization process is carried out in a polymerization reactor.The description of the polymerization process as preparing fluoropolymeror the dispersion thereof in the aqueous polymerization medium, alsoapplies to the preparation of fluoroplastics and perfluoroplastics asdispersions in the aqueous medium. The reactor is equipped with astirrer for the aqueous medium within the reactor to provide eventualsufficient interaction between free-radicals and monomers such as TFE atand after kickoff of the polymerization reaction for desirable reactionrates and uniform incorporation of comonomers if employed in thepolymerization reaction. The reactor preferably includes a jacketsurrounding the reactor so that the reaction temperature may beconveniently controlled by circulation of a controlled temperature heatexchange medium. The aqueous medium is preferably deionized anddeaerated water. The same is true for the water in any solution added tothe reactor, such as solutions containing polymerization initiator andstabilizing surfactant. The temperature of the reactor and thus of theaqueous medium will be from 25 to 120° C., preferably 40 to 120° C.,more preferably 50 to 120° C., even more preferably 60 to 120° C., andmost preferably 70 to 120° C. In operation, the reactor is pressured upwith fluoromonomer. Pressuring up the reactor is the addition offluoromonomer to the reactor to increase the reactor internal pressureto or near the pressure at which the polymerization reaction will becommenced and/or carried out (operating pressure). Typical pressures(operating pressure) that will be used will be from 30 to 1000 psig (0.3to 7.0 MPa), preferably from 1 to 800 psig (0.1 to 5.6 MPa). An aqueoussolution of free-radical polymerization initiator can then pumped intothe reactor in sufficient amount to cause kicking off of thepolymerization reaction. The kicking off (kickoff) of the polymerizationreaction is the commencement of polymerization. For simplicity, thiskicking off is indicated by a reduction in reactor pressure, e.g. by apressure drop of 10 psi (69 kPa), indicating the commencement offluoromonomer consumption in the polymerization process and therebycommencement of the polymerization reaction. This amount of pressuredrop is taken as meaning that the pressure drop is caused by theconsumption of fluoromonomer. One skilled in the art may rely on asmaller pressure drop if there is confidence that the smaller pressuredrop is not just a variation in internal reactor pressure that is notthe commencement of polymerization. One skilled in the art may rely on adifferent parameter altogether as indicating the commencement of thepolymerization. For example, in a pressure demand system, reduction inreactor pressure is immediately compensated by the flow of monomer intothe reactor to maintain pressure. In this system, the flow of a certainamount of pressure demand monomer into the reactor is considered toindicate commencement of the polymerization reaction. Whatever parameteris relied upon, the same parameter should be used from batch to batch soas to provide results, such as batch time, that are comparable.Relatively inactive fluoromonomer such as hexafluoropropylene (HFP),which is intended for copolymerization in the polymerization reaction,such as with TFE, can already be present in the reactor prior topressuring up with the more active TFE fluoromonomer. After kickoff,additional fluoromonomer is fed into the reactor to maintain theinternal pressure of the reactor at the operating pressure. The aqueousmedium is stirred to obtain the polymerization reaction rate and uniformincorporation of comonomer, if present.

As described in Process 2, the stabilization period is preferablysubsequent to the initial period. Addition of the hydrocarbon-containingstabilizing surfactant is delayed until after the kickoff has occurredin Process 1 and until the stabilization period in Process 2. The amount(timing) of the delay will depend on the surfactant being used and thefluoromonomer(s) being polymerized. The function of thehydrocarbon-containing surfactant in Process 1 and Process 2 is tostabilize the dispersion of fluoropolymer particles formed during thepolymerization process, hence the polymerization occurring in thepresence of this hydrocarbon-containing surfactant, includinghydrocarbon surfactant, being described as the stabilization period inProcess 2. Stabilization of the fluoropolymer particles means that theseparticles are dispersed within the aqueous medium during stirring ratherthan agglomerating with one another to form coagulum. Coagulum isundispersible fluoropolymer formed during the polymerization. Thisundispersible fluoropolymer consists of fluoropolymer if any, thatadheres to the interior wall of the reactor and all unadheredfluoropolymer that is not dispersed in the polymerization medium. Thisdispersion persists upon completion of the polymerization reaction andthe stirring discontinued. This disclosure of stabilization effect andthe description of coagulum with reference to fluoropolymer also applieswhen the fluoropolymer is the preferred fluoroplastic, most preferably,perfluoroplastic.

The polymerization process of the present invention preferably has twoconditions as mentioned above with respect to surfactant. First, at thetime of kickoff of the polymerization reaction in Process 1, the aqueouspolymerization medium is preferably essentially free of surfactant, bothwater-soluble hydrocarbon-containing surfactant (and hydrocarbonsurfactant) and halogen-containing surfactant (and fluorosurfactant).Second, the stabilizing surfactant, which is hydrocarbon-containingsurfactant, preferably hydrocarbon surfactant, is preferably not addedto the aqueous polymerization medium until after polymerization kickoffhas occurred in polymerization Process 1 and after the initial period inProcess 2.

With respect to the essential freedom from hydrocarbon-containingsurfactant, the amount of hydrocarbon-containing surfactant, includinghydrocarbon surfactant, that can be present in the aqueous medium priorto polymerization kickoff without being detrimental to thepolymerization reaction will depend on the particularhydrocarbon-containing surfactant. Generally such amount preferablyshould be no more than 50 ppm, preferably no more than 40, 30, 20 or 15ppm. The definition of ppm herein is given under the Examples. Moreover,such presence of the hydrocarbon-containing surfactant would not besufficient to stabilize the eventual dispersion of fluoropolymerparticles. Paraffin wax may be present in the aqueous medium to reducecoagulum formation. This is a hydrocarbon material that is notsufficiently water soluble to inhibit the polymerization reaction. Theseppm amounts also apply to the essential freedom from halogen-containingsurfactant, including fluorosurfactant, in the aqueous polymerizationmedium before kicking off of the polymerization reaction in Process 1and in the initial dispersion of fluoropolymer particles in the initialperiod of the polymerization process of Process 2. These ppm amountsalso apply to the polymerization reactor being essentially free ofhydrocarbon-containing compound in the initial period in accordance witha preferred form of Process 2. Most preferably the amount of any and allhalogen-containing surfactant, including fluorosurfactant, present inthe aqueous polymerization medium is no greater than 5 ppm, and mostpreferably, no halogen containing surfactant is added to thepolymerization reactor at any time during the practice of thepolymerization process of the present invention including theembodiments set forth as Processes 1 and 2.

With respect to the delay in adding the hydrocarbon-containingsurfactant to the aqueous medium as the stabilizing surfactant, thisdelay is beneficial in reducing any telogenic effect of the stabilizingsurfactant on the polymerization. This delay can be measured in terms ofthe concentration of fluoropolymer formed in the aqueous polymerizationmedium when addition of the stabilizing surfactant to the aqueous mediumcommences, and can be represented by the following equation:Concentration of fluoropolymer in wt %=([A÷(B+A)]×100,wherein A is the weight of dispersed fluoropolymer formed beforeaddition of the surfactant commences and B is the weight of water in thepolymerization reactor at the time stabilizing surfactant additioncommences. The water additions comprising B (in the equation above) tothe reactor may include dissolved ingredients, such as initiator. Forsimplicity, the water additions are each considered to be entirely ofwater as indicated by the calculations of the concentration offluoropolymer shown in Example 1. All the fluoropolymer that is formedis considered to be present in the aqueous medium. A is determined bythe amount (weight) of fluoromonomer consumed up until the time thesurfactant addition commences since no coagulum will have formed soearly in the polymerization reaction. When the fluoromonomer is themonomer that maintains the pressure (operating) of the polymerizationprocess within the reactor, the amount of fluoromonomer consumed is theamount fed to the reactor to maintain (makeup) this pressure untilstabilizing surfactant addition commences. When comonomer is present andits amount is not determined by makeup to maintain pressure, it isassumed that the incorporation of the comonomer into the fluoropolymeris uniform. The amount of polymer produced (A) can then be calculated bythe consumed fluoromonomer, e.g. TFE, fed to the reactor divided by thequantity 1 minus the weight fraction of comonomer in the fluoropolymer.B is the sum of the weight of all water additions to the reactor untilsurfactant addition commences. Thus, B includes the weight of theinitial amount of water charged to the reactor and all additional watercharges, such as in the form of solutions of nucleant surfactant, salt(if present), and oxidizing agent discussed in the sectionPolymerization Sites, initiator for kick off of the polymerizationreaction, and additional initiator pumped into the aqueous medium upuntil the time surfactant addition commences.

It has been found that premature addition of the hydrocarbon-containingstabilizing surfactant to the aqueous polymerization medium excessivelyinhibits the polymerizing of fluoromonomer to fluoropolymer. Thus, it ispreferred that the concentration of fluoropolymer in the aqueouspolymerization medium is at least 0.6 wt % when the surfactant additioncommences, more preferably at least 0.7, or at least 0.8, or at least 1wt %. Even more preferably, the fluoropolymer concentration is at least1.2 wt % and for melt fabricable fluoropolymer such as FEP and PFA, theconcentration is preferably at least 2 wt %, and for PTFE, theconcentration is preferably at least 1 wt %, more preferably at least1.6 wt %. These concentrations of fluoropolymer also apply tofluoroplastics and perfluoroplastics. The maximum delay in commencingthe metering of the stabilizing surfactant will depend on thefluoromonomer(s) being polymerized and the coagulum wt % consideredacceptable for the solids content of the dispersion to be obtained.

When addition of the hydrocarbon-containing stabilizing surfactant tothe aqueous polymerization medium begins, this addition is preferablydone by metering the surfactant into the aqueous medium at a rate thatreduces the telogenic activity of the stabilizing surfactant whilemaintaining surface activity to form a stable dispersion offluoropolymer, preferably fluoroplastic, more preferablyperfluoroplastic, particles in the aqueous polymerization medium.Preferably, the metering rate is 0.005 to 1.4 g/l-hr, more preferably0.005 to 1.0 g/l-hr, and even more preferably 0.01 to 0.8 g/l-hr. In theexpression g/l-hr, g is the weight in grams of the surfactant by itself,l is the reactor volume in liters, and hr is the unit of time. Thepreferred metering rate for high solids dispersions is set forth inEXAMPLE 10. The time increments for the addition of thehydrocarbon-containing stabilizing surfactant, including hydrocarbonsurfactant, are preferably at least every 20 minutes, preferably atleast every 10 min, more preferably at least every 5 min, and/or mostpreferably, continuously, during the polymerization reaction. The amountof such surfactant added and its timing of addition will depend on thefluoromonomer(s) being polymerized. Too little surfactant results inincreased coagulum, and too much surfactant slows down thepolymerization reaction and inhibits the growth of polymer chains. Eachof these metering rates can be used with each of the weight %concentrations of fluoropolymer, fluoroplastic, and perfluoroplasticmentioned above with respect to the commencement of the surfactantaddition. The metering rates apply to the surfactant, not to thesolution within which the surfactant is present as added to the aqueousmedium in the reactor.

With respect to the hydrocarbon-containing surfactant that is used inthe process of the present invention to stabilize the dispersion offluoropolymer, fluoroplastic, and perfluoroplastic particles formed bythe process, this surfactant is a compound that has hydrophobic andhydrophilic moieties, which enables it to disperse and stabilizehydrophobic entities such as the aforesaid particles, in an aqueousmedium. This definition also applies to surfactant that the aqueousmedium is as essentially free of at the carrying out of the steps (b)and (c) of the polymerization Process 1 and, in the preferred form ofProcess 2 in which the aqueous medium is essentially free ofwater-soluble hydrocarbon-containing compound after the preparation ofthe initial dispersion in the initial period, and the water-solublehydrocarbon-containing compound is selected from cationic surfactants,nonionic surfactant and anionic surfactants.

The hydrocarbon-containing stabilizing surfactant, including hydrocarbonsurfactant, is preferably an anionic surfactant. An anionic surfactanthas a negatively charged hydrophilic portion such as a carboxylate,sulfonate, or sulfate salt and a long chain hydrocarbon portion, such asalkyl as the hydrophobic portion. In the stabilization context,surfactants stabilize polymer particles by coating the particles withthe hydrophobic portion of the surfactant oriented towards the particleand the hydrophilic portion of the surfactant in the water phase. Theanionic surfactant adds to this stabilization, the feature of beingcharged to provide repulsion of the electrical charges betweenparticles. Surfactants typically reduce surface tension of the aqueousmedium containing the surfactant significantly.

One example anionic hydrocarbon surfactant is the highly branched C10tertiary carboxylic acid supplied as Versatic® 10 by ResolutionPerformance Products.

Another useful anionic hydrocarbon surfactant is the sodium linear alkylpolyether sulfonates supplied as the Avanel® S series by BASF. Theethylene oxide chain provides nonionic characteristics to the surfactantand the sulfonate groups provide certain anionic characteristics.

Another group of hydrocarbon surfactants are those anionic surfactantsrepresented by the formula R-L-M wherein R is preferably a straightchain alkyl group containing from 6 to 17 carbon atoms, L is selectedfrom the group consisting of —ArSO₃ ⁻, —SO₃ ⁻, —SO₄—, —PO₃ ⁻ and —COO⁻,and M is a univalent cation, preferably H⁺, Na⁺, K⁺ and NH₄ ⁺. —ArSO₃ ⁻is aryl sulfonate. Preferred of these surfactants are those representedby the formula CH₃—(CH₂)_(n)-L-M, wherein n is an integer of 6 to 17 andL is selected from —SO₃M, —PO₃M or —COOM and L and M have the samemeaning as above. Especially preferred are R-L-M surfactants wherein theR group is an alkyl group having 12 to 16 carbon atoms and wherein L issulfate, and mixtures thereof, such as sodium dodecyl sulfate (SDS). Forcommercial use, SDS (sometimes referred to as sodium lauryl sulfate), istypically obtained from coconut oil or palm kernel oil feedstocks, andcontains predominately sodium dodecyl sulfate but may contain minorquantities of other R-L-M surfactants with differing R groups.

Another group of surfactants are the siloxane surfactants. Siloxanesurfactants and polydimethylsiloxane (PDMS) surfactants in particular,are described in Silicone Surfactants, R. M. Hill, Marcel Dekker, Inc.,ISBN: 0-8247-00104. The structure of the siloxane surfactant comprisesdefined hydrophobic and hydrophilic portions, the hydrophilic portionimparting water solubility to the surfactant. The hydrophobic portioncomprises one or more dihydrocarbylsiloxane units:

wherein the substitutions on the silicon atoms in the siloxane chain areentirely hydrocarbyl. In the sense that the carbon atoms of thehydrocarbyl groups are entirely substituted with hydrogen atoms wherethey could be substituted by halogen such as fluorine, these siloxanesurfactants can also be considered as hydrocarbon surfactants, i.e. themonovalent substituents on the carbon atoms of the hydrocarbyl groupsare hydrogen

The hydrophilic portion of the siloxane surfactant may comprise one ormore polar moieties including ionic groups such as sulfate, sulfonate,phosphonate, phosphate ester, carboxylate, carbonate, sulfosuccinate,taurate (as the free acid, a salt or an ester), phosphine oxide,betaine, betaine copolyol, or quaternary ammonium salt.

Examples of hydrocarbon surfactants that are siloxane-based and that areanionic are such surfactants available from Noveon Consumer Specialties,Inc, a division of Lubrizol Advanced Materials, Inc., as follows:

Another example of anionic hydrocarbon surfactant useful in the presentinvention is the sulfosuccinate surfactant Lankropol® K8300 availablefrom Akzo Nobel Surface Chemistry LLC. The surfactant is reported to bethe following:

Butanedioic acid, sulfo-,4-(1-methyl-2-((1-oxo-9-octadecenyl)amino)ethyl)ester, disodium salt;CAS No.: 67815-88-7

Additional sulfosuccinate hydrocarbon surfactants useful in the presentinvention are diisodecyl sulfosuccinate, Na salt, available asEmulsogen® SB10 from Clariant, and diisotridecyl sulfosuccinate, Nasalt, available as Polirol® TR/LNA from Cesapinia Chemicals.

The preferred hydrocarbon surfactants as the stabilizing surfactant inthe polymerization process are the anionic surfactants, and the mostpreferred of these surfactants are the R-L-M surfactants describedabove, especially sodium dodecyl sulfate (SDS).

With respect to the water-soluble free-radical polymerization initiatorused in the polymerization process of the present invention (step (c)described in Process 1 and causing the polymerizing, especially in thestabilization period of Process 2, this initiator is added to theaqueous polymerization medium in the reactor to cause the polymerizationreaction in the pressured-up reactor to kickoff. The amount of initiatoradded will depend on the fluoromonomer being polymerized. Preferredinitiators are the highly active water-soluble salts of inorganicinitiators such as the inorganic peracids. Preferred initiators are thepersulfate salts, e.g., ammonium persulfate or potassium persulfate.Preferred persulfate initiators are substantially free of metal ions andmost preferably are ammonium salts. For polymerization of TFE to PTFE,however, the preferred initiator is organic peracid such as disuccinicacid peroxide (DSP), which is highly inactive, thereby requiring a largeamount to cause kickoff, e.g. at least 600 ppm, together with a highlyactive initiator, such as inorganic persulfate salt, in a smalleramount. The activity of the initiator refers to the ability of theinitiator to form free radicals capable of initiating polymerization inthe aqueous polymerization medium at the temperature of the mediumwithin the reactor, from 25, 40, 50, 60 or 70 to 120° C., referred toabove, at which the polymerization reaction is carried out. Theselection of initiator and polymerization temperature is preferablymatched so that the free-radicals arising from the initiator are causedby the temperature of the aqueous medium, whether the free radicals arethermally induced or their formation is assisted by the presence ofpromoter or reducing agent. The polymerization initiator is preferablyfree of alkali metal ion. The initiator added to cause kickoff can besupplemented by additional initiator as may be necessary as thepolymerization reaction proceeds.

The amount and identity of fluoromonomer present at kickoff will dependon the fluoropolymer, fluoroplastic, or perfluoroplastic being made. Inthe case of modified PTFE, the modifying monomer will generally all beadded at the time of the precharge to the reactor. The same can be truefor comonomer used in the polymerization with TFE to form meltprocessible fluoroplastics, although comonomer can be added as thepolymerization reaction proceeds. Once polymerization begins, additionalTFE (and comonomer, if any) is added to maintain the reactor pressuredesired. Chain transfer agents can be added when molecular weightcontrol is desired For some polymerizations, additional polymerizationinitiator may be added during the polymerization.

After completion of the polymerization (typically several hours) whenthe desired amount of polymer or solids content has been achieved,agitation and the feeds are stopped. This stopping of agitation andstopping of fluoromonomer feed is the completion of the polymerizationreaction. The reactor is vented, and the raw dispersion offluoropolymer, including fluoroplastic and perfluoroplastic particles inthe reactor is transferred to a cooling or holding vessel. Thus, thepolymerization process is a batch process.

The solids content of the aqueous dispersion, which is the dispersion ofthe aforesaid particles produced by the process of the invention, ispreferably at least 10% by weight, preferably at least 16 wt %. Morepreferably, the fluoropolymer, including fluoroplastic, orperfluoroplastic solids content is at least 20% by weight. Solidscontents up to 33-35 wt % are obtainable by any process of the presentinvention. Surprisingly, much higher solids contents, e.g. of 45 wt %and greater than 45 wt % are also obtainable as described in EXAMPLE 10.Solids contents up to 60 wt % and even up to 65 wt % are obtainable.Solids content is the weight % of these fluoropolymer particlesdispersed in the aqueous medium, based on the combined weight of theseparticles and total water added to the reactor. The total water is thetotal amount of water added during polymerization process, including anywater added to the reactor prior to kickoff of the polymerizationreaction. The calculation of wt % solids content is as follows:100×[weight of fluoropolymer particles in the dispersion÷(weight of saidfluoropolymer particles+total weight of water)]. Solutions ofingredients added to the aqueous medium, such a initiator solution, areconsidered to be entirely water in the calculation of solids content.The preferred particle size (Dv(50)) of the fluoropolymer, includingfluoroplastic and perfluoroplastic particles in the aqueous dispersionthereof is preferably from 100 to 300 nm.

Preferably, the amount of fluoropolymer, including fluoroplastic andperfluoroplastic present as coagulum formed by the polymerization is nogreater than 5 wt % of the total amount of fluoropolymer, fluoroplastic,or perfluoroplastic, respectively, made. In the preferred process of theinvention, polymerizing produces no greater than 3 wt %, or no greaterthan 2 or 1 wt %, most preferably no greater than 0.5 wt % of suchpolymer present as coagulum. More preferably, the amount of coagulum isless than each of these amounts. The maximum solids content ispreferably controlled to minimize coagulum to an amount described above.

The as-polymerized dispersion can be transferred to a dispersionconcentration operation which produces concentrated dispersionsstabilized typically with nonionic hydrocarbon surfactants by knownmethods. Hydrocarbon surfactant can be used for this purpose because theconcentration of the dispersion in the aqueous medium is carried outafter completion of the polymerization. Solids contents of concentrateddispersion is typically 35 to 70% by weight, more often 45 to 65 wt %.EXAMPLE 10 discloses solids contents above 45 wt % being obtaineddirectly from polymerization, thereby not requiring any concentrationstep. Alternatively, for use as a molding resin, a fluoropolymer resinis isolated from the fluoropolymer dispersion usually by coagulation andthe aqueous medium is removed. The fluoropolymer is dried then processedinto a convenient form such as flake, chip or pellet for use insubsequent melt-processing operations. Certain grades of PTFE dispersionare made for the production of fine powder. For this use, the dispersionis coagulated, the aqueous medium is removed and the PTFE is dried toproduce fine powder.

Passivation of the Hydrocarbon-Containing Surfactant

In a preferred embodiment of any of the embodiments of polymerizationprocesses of the present invention disclosed herein, thehydrocarbon-containing surfactant used to stabilize the dispersion offluoropolymer, including fluoroplastic and perfluoroplastic, particles,is passivated. It is also preferred that the passivated stabilizingsurfactant is anionic. Passivation is the treatment of thehydrocarbon-containing surfactant to reduce its telogenicity.

In one embodiment, the stabilizing surfactant as metered (added) intothe aqueous polymerization medium is passivated prior to metering(addition) into the aqueous medium. Preferably, the passivatedstabilizing surfactant is the reaction product of this surfactant and anoxidizing agent such as hydrogen peroxide. The reaction forming thisreaction product is preferably conducted in an aqueous medium at atemperature of no greater than 50° C. This temperature of reaction is incontrast to the temperature of the aqueous medium within which thepolymerization reaction is most often carried out, i.e. at a temperatureof at least 60° C.

The reduction in telogenicity of the stabilizing surfactant resultingfrom passivation provides improvements including one or more of thefollowing: 1) reducing the polymerization time to produce the desiredfluoropolymer solids content in the aqueous medium, without anyappreciable increase in coagulum and/or 2) reducing the time of delayafter kickoff before the stabilizing surfactant can be added to theaqueous medium. Thus, passivation preferably increases the effectivenessof the surfactant. While telogenicity is reduced by passivation, thepassivated surfactant still performs its surfactant function ofstabilizing the dispersion of fluoropolymer particles in the aqueousmedium.

Passivation can be carried out by reacting the stabilizing surfactantwith hydrogen peroxide in aqueous solution. A passivation adjuvant forthe oxidation reaction is preferably also used to accelerate (catalyze)the oxidation reaction. This adjuvant is preferably metal ion that ispreferably provided in a form which is soluble in the aqueous medium inthe polymerization reactor. This solubility can be achieved by the metalion being in salt form, i.e. the metal ion is the cation of the salt.Preferably the salt is inorganic and the anion of the salt can be anyanion that provides this solubility, with or without water of hydrationincluded in the salt. The anion, however, should not have an adverseeffect on the polymerization reaction or fluoropolymer product. Examplesof preferred anions of the metal salt include sulfate, sulfite, andchloride.

Preferably, the metal of the metal ion has multiple positive valences,sometimes referred to as multiple oxidation states. Examples of metalion catalysts for the oxidation with hydrogen peroxide include Fe, Mnand Cu.

Even with acceleration, the oxidation reaction using hydrogen peroxideas the oxidizing agent is slow, taking for example at least 30 min. tocompletion. A procedure for carrying out the oxidation can be asfollows: A solution of the stabilizing surfactant in water is formed.The Fe⁺² metal ion as iron sulfate hydrate passivation adjuvant is addedand dissolved in this solution. The pH of the solution can be adjustedby addition of appropriate reagent to promote the oxidation reaction.The solution is agitated and hydrogen peroxide is slowly added to thesolution. The weight ratio of peroxide, to Fe⁺² can be generally from20:1 to 400:1, preferably from 30:1 to 300:1 and more preferably from60:1 to 200:1. The weight ratio of peroxide to stabilizing surfactant,such as SDS, can be from 0.15:1 to 3.5:1, preferably from 0.3:1 to2.6:1, and more preferably, from 0.5:1 to 1.6:1. Upon completion of theoxidation reaction, the resultant aqueous solution can be used foradding the passivated surfactant to the aqueous polymerization mediumduring the polymerization reaction in the manner described above. Thus,the water of the aqueous solution is preferably deaerated and deionized,as is done for the aqueous polymerization medium, so that the wateradded to the reactor along with the passivated surfactant is notdetrimental to the polymerization reaction or the fluoropolymerobtained. These proportions of reactants and passivation adjuvant, ifpresent, apply to the passivation of any and all thehydrocarbon-containing and hydrocarbon surfactants mentioned above forstabilization of the fluoropolymer particle dispersion.

When prepared separately from the aqueous polymerization medium, thepassivated surfactant is uniform in its composition within the aqueoussolution within which the passivation reaction is carried out. Thismeans that the composition of the passivated surfactant fed into thereactor aqueous medium is the same at the end of the polymerizationreaction as the composition at the commencement of its feed to thereactor.

Use of hydrogen peroxide to passivate the stabilizing surfactant doesnot create any salt that would accompany the feed of the passivatedsurfactant solution to the reactor. Salt when present in sufficientamount during the polymerization reaction can be detrimental, such as bycausing increased coagulum.

The temperature of the aqueous solution within which the passivationreaction is carried out using hydrogen peroxide as the oxidizing agentis important. The preferred temperature range that is effective forcausing the peroxide to react oxidatively with the stabilizingsurfactant is 1 to 50° C., preferably 5 to 45° C. and most preferably 10to 45° C. As the temperature increases from 45° C., reactivity falls offsharply and is virtually non-existent at temperatures above 50° C. Thus,the desired passivation effect is not obtained at the usualpolymerization temperatures of 60° C. and higher. The passivationreaction using hydrogen peroxide as the oxidizing agent is thereforepreferably carried out separately from the aqueous polymerizationmedium.

The passivation effect is determined by conducting the oxidationreaction between the stabilizing surfactant and hydrogen peroxide atdifferent aqueous solution temperatures and thereafter using thepassivated surfactant as the stabilizing surfactant added to the aqueouspolymerization medium in the polymerization of fluoromonomer, andcomparing the polymerization (batch) times required to obtain a givenfluoropolymer, including fluoroplastic and perfluoroplastic, solidscontent in the aqueous polymerization medium. Preferably the passivationis effective such that the batch time is decreased by at least 10%,preferably at least 20%, more preferably at least 35% and mostpreferably at least 50%. Batch time is the time from polymerizationkickoff until completion of the polymerization reaction for a givensolid content result of the polymerization reaction. When differentsolids contents of the aqueous dispersion of these fluoropolymerparticles are being prepared, productivity is better measured byspace-time yield (STY) of the polymerization reaction. In STY, space (S)is the volume of the reactor, time (T) is the time from kickoff of thepolymerization reaction until completion, and yield (Y) if the weight ofdispersed fluoropolymer formed. STY is expressed herein as gm (ofdispersed fluoropolymer)/l-hr. The increased STY resulting from thepassivation of the stabilizing surfactant can be characterized by thesame percents as stated earlier in this paragraph.

In another embodiment, the stabilizing surfactant is passivated priorto, during, or after addition to the aqueous medium in thepolymerization reactor using a different oxidizing agent than hydrogenperoxide, each of these being preferred timing for the passivationreaction. In effect, this timing of the passivation is the passivationoutside the reactor and inside the reactor. Passivation is preferablycarried out during or after addition to the aqueous reactor. Passivationmost preferably is carried out after the surfactant enters the reactor,so the passivation in the aqueous medium occurs within the reactor. Inthis embodiment, the passivated stabilizing surfactant is the reactionproduct of this surfactant and as the oxidizing agent, water-solublepolymerization initiator, preferably the initiator being used to causethe polymerization reaction to form the dispersion of fluoropolymer,including fluoroplastic and perfluoroplastic particles in the aqueousmedium. In this embodiment of the process, passivation is preferablycarried out at the same temperature as the polymerization, preferably inthe range of from 25, 40, 50, 60 or 70 to 120° C., as mentioned above.

Preferably, this passivation reaction is carried out in the presence ofpassivation adjuvant, which is preferably metal ion supplied to thisreaction in the form described above with respect to the metal ion usedto catalyze the reaction between the oxidizing agent and the stabilizingsurfactant. Experimentation has shown that the presence of the metal ioncan reduce batch time by 66% and increase STY by 300%.

Preferred metal ions include those of Groups 2-12 of the Periodic Tableof the Elements. Such Periodic Table is that which is disclosed on theback of the front cover of M. S. Silverberg, Chemistry, The MolecularNature of Matter and Change, 5 Ed., published by McGraw-Hill HigherEducation (2009). The Group numbering for this Table is 1 to 18 inaccordance with 2010 IUPAC format, sometimes called “new notation”. ThisGroup numbering is referred to herein. This Group numbering applies tovertical columns of elements in the Periodic Table.

The most preferred metal ions are the transition metals, notably thosein Groups 3-12 and of these, the most preferred are those in Groups6-12, even more preferred Groups 7-12 and most preferred those in Groups7-11. The Periodic Table also has horizontal grouping of elements calledPeriods that are numbered 1-7, starting with H of the Group 1 elementsand ending with Fr of the Group 1 elements as Period 7. Among thetransition metals, those in the horizontal Period 4 are most preferred.Included in the term “transition metals” are the “inner transitionmetal, i.e. the lanthanides and the actinides.

Preferred transition metals include Mn, Fe, Co, Ni, Cu, Zn, Ce, and Ag,with Fe and Cu being most preferred. One of the characteristics of mostof the transition metals preferably used in the present invention isthat they have multiple positive valences, sometimes referred to asmultiple oxidation states. Fe, for example has valences of +2 and +3,and Cu has valences of +1 and +2. The most preferred metal ions areferrous ion and cuprous ion. The metal ions used to catalyze thepolymerization initiator/stabilizing surfactant oxidation reaction canalso be used to catalyze the oxidation of the stabilizing surfactant ingeneral, including when hydrogen peroxide is the oxidizing agent. Theselection of metal ion will depend on the oxidizing agent used. Forhydrogen peroxide, the preferred metal ions are the ions of Fe, Mn, andCu.

When the oxidizing agent is polymerization initiator, the salt providingthe metal ion can be added to the aqueous medium in the polymerizationreactor as an aqueous solution together with the aqueous solution ofstabilizing surfactant or independent therefrom, metered into theaqueous medium along with metering of the surfactant into the aqueousmedium, metered independently into the aqueous medium, or added all atone time to the aqueous medium. If the polymerization reaction ispreceded by the formation of hydrocarbon-containing polymerization sitesas will be described hereinafter, the addition of the passivationadjuvant as metal ion to the aqueous medium is preferably delayed untilafter the formation of these sites has at least commenced to avoid theformation of excessive coagulum. Thus, addition of the metal ion aspassivation adjuvant to the aqueous medium is preferably delayed untilafter commencement (kick off) of the polymerization reaction.

The rapidity of the passivation reaction using polymerization initiatortogether with passivation adjuvant, enables this passivation reaction tobe carried out prior to, during or after addition of the stabilizingsurfactant to the aqueous medium in the polymerization reactor. The“prior to” passivation reaction can be carried out in the holding vesselfor the aqueous solution of the stabilizing surfactant, by adding thepassivation adjuvant and polymerization initiator to this vessel. The“during” passivation reaction can be carried out by co-feeding aqueoussolutions of the stabilizing surfactant, passivation adjuvant, andpolymerization initiator together into the reactor such that thesesolutions intermix during the addition to the reactor. The passivationreaction during this intermixing is believed to at least commence if notbe completed, depending on the length of the reactor feed linecontaining all three ingredients. The “after” passivation reaction, i.e.passivation within the aqueous medium in the polymerization reactor, isdescribed in the preceding paragraph.

In both passivation embodiments, the hydrocarbon-containing surfactant,including hydrocarbon surfactant, is passivated by reacting thesurfactant with an oxidizing agent. In both passivation reactions, theoxidation reaction is preferably carried out in the presence ofpassivation adjuvant, which is preferably metal ion, in the aqueousmedium, which catalyzes the oxidation reaction. The metal ion preferablyhas multiple positive valences, and the preferred metal ions will dependon which oxidizing agent is used as described above. In this regard, thepreferred oxidizing agents are hydrogen peroxide or water-solublepolymerization initiator, preferably selected from those disclosed inthe section entitled Polymerization Process. The timing of thepassivation reaction will depend on the oxidizing agent used and ispreferably either prior to the addition of the stabilizing surfactant tothe reactor, i.e. the aqueous medium in the reactor, or during thisaddition to the reactor, or after this addition to the reactor.

The passivation adjuvant used in either passivation embodiment of thepresent invention is preferably very small. For example, theconcentration of passivation adjuvant, which can be metal ion, ispreferably no greater than 2 wt %, based on the weight of thehydrocarbon-containing, including hydrocarbon, surfactant in the aqueousmedium at the completion of the polymerization reaction. The amount ofpassivation adjuvant, which can be metal ion, in the aqueous medium uponcompletion of polymerization is preferably no greater than 25 ppm, basedon the amount of water present in the reactor upon completion of thepolymerization. These amounts also apply when other passivationadjuvants are used, i.e. to the moiety thereof that enhances thereduction in telogenic behavior benefit to the hydrocarbon-containingsurfactant, including hydrocarbon surfactant as a result of passivation.

Polymerization Sites

A preferred embodiment is to provide polymerization sites in the aqueousmedium prior to kickoff of the polymerization process, in order toreduce the size of the fluoropolymer particles forming the dispersionthereof in the aqueous medium as a result of the polymerization process.The polymerization sites form loci for the precipitation offluoropolymer, the number of loci being greater than if no such siteswere present, thereby resulting in the smaller fluoropolymer particlesize for a given percent solids. After this precipitation, thesubsequent precipitation of fluoropolymer is preferably at the sameloci, causing the polymer particles to grow, until the end of thepolymerization reaction. This effect of polymerization sites is alsoapplicable to fluoroplastic and perfluoroplastic and the growingparticles of fluoroplastic or perfluoroplastic resulting from thepolymerization. The polymerization sites are the precursor to theinitial dispersion of fluoropolymer particles described in Process 2

One method of forming these polymerization sites is to start withalready polymerized particles present in the aqueous polymerizationmedium prior to kickoff of the polymerization reaction. These alreadypolymerized particles are often called polymer seeds. The seeds may beformed by free-radical initiated polymerization of fluoromonomer in thepresence of surfactant so that the polymer seeds remain dispersed in theaqueous medium within which they are formed. The subsequent kickoff ofthe polymerization reaction in the aqueous medium wherein the dispersionof polymer seeds are already present involves adding new fluoromonomer,i.e. fluoromonomer in the present invention, and new polymerizationinitiator to the reactor to cause the kickoff and subsequentpolymerization.

The surfactant used to disperse the polymer seeds in the aqueous mediumcan be a halogen-containing surfactant, such as a fluorosurfactant, thathas minimal to no telogenic activity, thereby not inhibiting thesubsequent kickoff and polymerization reaction forming thefluoropolymer, fluoroplastic, or perfluoroplastic described in Process 1or the polymerizing thereof occurring during the stabilization perioddescribed in Process 2. This halogen-containing surfactant may bepresent due to its use during polymerization of the polymer seeds.Examples of fluorosurfactants are ammonium perfluorooctanoate, ammoniumω-hydrohexadecafluorononoate, and ammonium 3,6dioxa-2,5-di(trifluoromethyl)undecafluorononoate as disclosed in U.S.Pat. No. 3,391,099. Examples of suitable fluoroether surfactants havebeen described in U.S. Pat. No. 3,271,341 to Garrison; U.S. patentpublications 2007/0015864, 2007/0015865, and 2007/0015866 to Hintzer etal.; U.S. patent publications 2005/0090613 to Maruya et al. and2006/0281946 to Morita et al.; PCT patent publications WO 2007046345 toHiguchi et al., 2007046377 to Funaki et al., 2007046482 to Hoshikawa etal., and 2007/049517 to Matsuoka et al. Additional fluorosurfactants aredisclosed in U.S. Pat. No. 7,705,074 (Brothers et al.), which are thecombination of a fluoropolyether having a number average molecularweight of at least 800 g/mol and a short chain fluorosurfactant havingthe formula[R¹—O_(n)-L-A⁻]Y⁺  (I)wherein:

-   -   R¹ is a linear or branched partially or fully fluorinated        aliphatic group which may contain ether linkages;    -   n is 0 or 1;    -   L is a linear or branched alkylene group which may be        nonfluorinated, partially fluorinated or fully fluorinated and        which may contain ether linkages;    -   A⁻ is an anionic group selected from the group consisting of        carboxylate, sulfonate, sulfonamide anion, and phosphonate; and    -   Y⁺ is hydrogen, ammonium or alkali metal cation; with the        proviso that the chain length of R¹—O_(n)-L- is not greater than        6 atoms.

“Chain length” as used in this application refers to the number of atomsin the longest linear chain in the hydrophobic tail of thefluorosurfactant employed in the process of this invention. Chain lengthincludes atoms such as oxygen atoms in addition to carbon in the chainof hydrophobic tail of the surfactant but does not include branches offof the longest linear chain or include atoms of the anionic group, e.g.,does not include the carbon in carboxylate. “Short chain” as used inthis application refers to a chain length of not greater than 6. “Longchain” refers to a chain length of greater than 6, e.g.,fluorosurfactants having a chain length of 7 to 14 atoms.

Preferably, the chain length of R¹—O_(n)-L- is 3 to 6 atoms. Inaccordance with one preferred form of the invention the chain length ofR¹—O_(n)-L- is 4 to 6 atoms. In accordance with another preferred formof the invention the chain length of R¹—O_(n)-L- is 3 to 5 atoms. Mostpreferably, the chain length of R¹—O_(n)-L- is 4 to 5 atoms.

The preferred short chain surfactant is the dimer acid ofhexafluoropropylene epoxide, having the formula C₃F₇O—CF(CF₃)—COOH.

The perfluoropolyether (PFPE) acids or salts thereof can have any chainstructure in which oxygen atoms in the backbone of the molecule areseparated by saturated fluorocarbon groups having 1-3 carbon atoms. Morethan one type of fluorocarbon group may be present in the molecule.Representative structures have the repeat unit represented in thefollowing formulas:(—CFCF₃—CF₂—O—)_(n)  (VII)(—CF₂—CF₂—CF₂—O—)_(n)  (VIII)(—CF₂—CF₂—O—)_(n)—(—CF₂—)—)_(m)  (IX)(—CF₂—CFCF₃—O—)_(n)—(—CF₂—O—)_(m)  (X)These structures are discussed by Kasai in J. Appl. Polymer Sci. 57, 797(1995). As disclosed therein, such PFPE can have a carboxylic acid groupor salt thereof at one end or at both ends. Similarly, such PFPE mayhave a sulfonic acid or phosphonic acid group or salt thereof at one endor both ends. In addition, PFPE with acid functionality at both ends mayhave a different group at each end. For monofunctional PFPE, the otherend of the molecule is usually perfluorinated but may contain a hydrogenor chlorine atom. PFPE having an acid group at one or both ends for usein the present invention has at least 2 ether oxygens, preferably atleast 4 ether oxygens, and even more preferably at least 6 etheroxygens. Preferably, at least one of the fluorocarbon groups separatingether oxygens, and more preferably at least two of such fluorocarbongroups, have 2 or 3 carbon atoms. Even more preferably, at least 50% ofthe fluorocarbon groups separating ether oxygens have 2 or 3 carbonatoms. Also, preferably, the PFPE has a total of at least 15 carbonatoms, e.g., the preferred minimum value of n or n+m in the above repeatunit structures is at least 5. More than one PFPE having an acid groupat one or both ends can be used in a process in accordance with theinvention. Typically, unless extraordinary care is employed tomanufacture a single specific PFPE compound, the PFPE may containmultiple compounds in varying proportions within a molecular weightrange about the average molecular weight. The number average molecularweight of the fluoropolyether acid or salt preferably has a numberaverage molecular weight of less than 6000 g/mol.

Because the seed polymer is small in particle size, e.g. 1 to 50 nm,only a small amount of fluorosurfactant is necessary to maintain thepolymer seeds as a dispersion until kickoff of the subsequentpolymerization reaction, whereby the aqueous medium prior to kickoff ofthe polymerization reaction or in the initial period of thepolymerization reaction is essentially free of halogen-containingsurfactant (as described above), including fluorosurfactant. This meansthat removal or recovery of the fluorosurfactant, if desired, from theaqueous polymerization medium after completion of the polymerization toform the dispersion of fluoropolymer particles can be minimized.

Another Example of providing polymer as polymerization sites isdisclosed in U.S. Patent Publication 2010/0160490 (Leffew et al.),wherein the polymerization sites are dispersed particulates offluorinated ionomer.

The precipitation of polymerized fluoromonomer on these polymericpolymerization sites prior to the addition of stabilizing surfactant tothe aqueous medium in the reactor can be used to provide the initialdispersion of fluoropolymer particles as described in Process 2.

Preferably, polymerization sites are hydrocarbon-containing as can beprovided by oleophilic nucleation sites formed in the aqueous mediumprior to kickoff of the polymerization as described in Process 1. Theseoleophilic nucleation sites are dispersed in the aqueous medium,enabling the precipitation of fluoropolymer, including fluoroplastic, atthese sites to be finely dispersed, such that the metering of thehydrocarbon-containing stabilizing surfactant can be delayed withoutpenalty in polymerization results. The oleophilic nucleation sites arepreferably formed by the addition of small amounts of water-solublehydrocarbon-containing compound, preferably hydrocarbon-containingsurfactant containing hydrophobic moiety and hydrophilic moiety, anddegradation agent, preferably an oxidizing agent, to the aqueous mediumprior to the kickoff of polymerization. This degradation agent subjectsthe hydrocarbon-containing compound to a reaction that degrades thehydrophilic moiety, thereby enabling the hydrophobic moiety of thesurfactant to become the oleophilic nucleation sites and the sites to behydrocarbon-containing. These oleophilic nucleation sites dispersed inthe aqueous medium are not polymer seeds. Thus, these sites, as formed,are preferably free of polymerized fluoromonomer.

The precipitation of polymerized fluoromonomer on these oleophilicnucleation sites prior to the addition of stabilizing surfactant to theaqueous medium in the reactor is another embodiment for providing theinitial dispersion of fluoropolymer particles as described in Process 2.

The water-soluble hydrocarbon-containing compound from which theoleophilic nucleation sites are derived is preferably a surfactant.Surfactants are well known to containing hydrophobic and hydrophilicmoieties, whereby they are also water soluble. The preparation ofoleophilic nucleation sites, while applicable to water-solublehydrocarbon-containing compounds in general, will be described withreference to the preferred hydrocarbon-containing surfactants, includinghydrocarbon surfactants.

The preferred degradation of the hydrophilic moiety of thehydrocarbon-containing compound, preferably surfactant, causes thesurfactant to lose hydrophilicity and its surfactant effect. Thisprovides the condition described above of the subsequent kickoff of thepolymerization reaction being carried out essentially free ofhydrocarbon-containing surfactant (and hydrocarbon surfactant).Accordingly, the dispersion of oleophilic nucleation sites are alsoessentially free of hydrocarbon-containing surfactant (and hydrocarbonsurfactant). No surfactant is necessary for the maintenance of theoleophilic nucleation sites as a dispersion until subsequent kickoff ofthe polymerization reaction.

A small amount of surfactant can, however, be present with thedispersion of oleophilic nucleation sites, if not detrimental to thekickoff of the polymerization reaction, whereby the dispersed oleophilicnucleation sites are essentially free of hydrocarbon-containingsurfactant, including hydrocarbon surfactant, as described above. Theamount that can be tolerated will depend on the surfactant.

In addition to the dispersion of oleophilic nucleation sites and theaqueous medium containing this dispersion being essentially free ofhydrocarbon-containing surfactant, it is preferred that this dispersionand aqueous medium are also essentially free of halogen-containingsurfactant, i.e. essentially free of all surfactant, as described above.If halogen-containing surfactant such as fluorosurfactant is present,then its amount should be small as described above, and most preferably,none is present.

The use of hydrocarbon-containing surfactant and especially hydrocarbonsurfactant as the precursor for the oleophilic nucleation sites in thedegradation reaction prior to polymerization kickoff provides ahalogen-free system in the aqueous polymerization medium for thecreation of the nucleation sites and the stabilization of thefluoropolymer particle dispersion subsequently obtained when thestabilizing surfactant is hydrocarbon surfactant.

The presence of the dispersion of oleophilic nucleation sites withoutthe assistance of surfactant to maintain these sites is unexpected. Thiscontradictory condition can be achieved, however, by how the sites areformed. The dispersion of oleophilic nucleation sites is preferablyformed by degrading a water-soluble hydrocarbon-containing compound,preferably that which is a surfactant, that contains hydrophilic moietyimparting water solubility to the surfactant and hydrophobic moiety.Thus, these sites are the product of the degradation reaction.Preferably the oxidizing agent causing the degradation reaction can be asmall amount of polymerization initiator added to the aqueous mediumafter the compound, preferably surfactant, addition. The degradationreaction is thus, preferably, an oxidation reaction. Prior to thisdegradation, the hydrophilic moiety of the compound, preferably thesurfactant, cloaks the hydrophobic moiety with hydrophilicity, therebyallowing the compound, preferably surfactant, to be water soluble.Degradation of the water-soluble hydrocarbon-containing compound,preferably hydrocarbon containing surfactant (compound/surfactant),degrades the hydrophilicity of the compound/surfactant, i.e. thehydrophilic moiety of the compound/surfactant, thereby being effectiveto enable the hydrophobic moiety of the hydrocarbon-containingcompound/surfactant to become the well dispersed oleophilic nucleationsites. Thus, these sites are hydrocarbon-containing oleophilicnucleation (polymerization) sites. If hydrocarbon compound, preferablysurfactant, is the precursor to the nucleation sites, then they arehydrocarbon oleophilic nucleation sites. These sites are accessible toand have an affinity for the precipitating fluoropolymer formed at thekicking off of the polymerization process. The preferred precursor tothe nucleation sites is hydrocarbon surfactant and the preferrednucleation sites are the hydrocarbon nucleation sites.

That the nucleation sites do not flocculate upon the degradation of thehydrophilicity of the compound is a result of the oleophilic nucleationsites being derived from a hydrocarbon-containing compound, preferablysurfactant, that is soluble in the aqueous medium. The distribution ofthe dissolved hydrocarbon-containing compound/surfactant is on amolecular basis within the aqueous medium. The oleophilic nucleationsites obtained from the compound/surfactant enjoy this samedistribution, thereby not requiring compound which is a surfactant tomaintain the dispersion of oleophilic nucleation sites.

To distinguish the hydrocarbon-containing stabilizing surfactant fromthe hydrocarbon-containing surfactant or hydrocarbon surfactantpreferably used as a precursor to the dispersion of oleophilicnucleation sites, the precursor surfactant can be referred to as thenucleant surfactant

The performance of the nucleation sites is judged primarily by the smallparticle size of the fluoropolymer, fluoroplastic, or perfluoroplasticparticles as compared to conducting the polymerization reaction withoutthese nucleation sites being present. This performance indicates thepresence of a dispersion of nucleation sites at the time ofpolymerization kickoff.

To obtain the pre-kick off condition of the dispersion of oleophilicnucleation sites and the aqueous polymerization medium being essentiallyfree of hydrocarbon-containing compound, preferablyhydrocarbon-containing surfactant, and preferably any other surfactantfrom the dispersion, preferably only a small amount (weight) of thehydrocarbon-containing surfactant as the nucleant surfactant is used asthe nucleation site precursor, e.g. no more than 50 ppm. When the eventis the dispersion of nucleation sites in the aqueous medium, the amountof water is that which is associated with the presence of the dispersionof these sites. This does not include after-added water such as in theform of the aqueous solutions of polymerization initiator added to causepolymerization kickoff and stabilizing surfactant used to stabilize thefluoropolymer particles formed after kickoff. The combination of a smallamount of nucleant surfactant (and hydrocarbon-containing compound)together with the oxidative degradation of the hydrophilicity thereofprovides the reduction in telogenicity.

The small amount of hydrocarbon-containing compound, preferably nucleantsurfactant, added to the aqueous medium to form the oleophilicnucleation sites is preferably no greater than 40 ppm, even morepreferably, no greater than 30 ppm, and most preferably no greater than20 ppm. The ppm amounts of oleophilic nucleating sites present in theaqueous medium would be less than the ppm amounts disclosed herein asbeing added to the aqueous medium by virtue of the degradation oroxidation reaction degrading the hydrophilic moiety. The same is truefor the hydrocarbon-containing compound after degradation, it no longerbeing the originally added compound. Thus, the amount of nucleationsites would be less than the 50 ppm, 40 ppm, 30 ppm, and 20 ppm amounts,respectively, mentioned above. Since it is believed that nucleationsites exist as molecules, only a small amount of thehydrocarbon-containing compound, preferably nucleant surfactant, canproduce a large amount of oleophilic nucleation sites. Thus, addition ofas little as 1 ppm of such compound/surfactant to the aqueous medium canprovide beneficial effect. The foregoing amounts apply to the use ofwater soluble hydrocarbon compounds and to hydrocarbon-containingsurfactant and hydrocarbon surfactant as nucleant surfactants andprecursors in the degradation reaction and to the resultanthydrocarbon-containing and hydrocarbon oleophilic nucleation sites aswell. The hydrocarbon-containing compounds and nucleant surfactants canbe used individually or in combination.

The water soluble hydrocarbon-containing compounds, preferably nucleantsurfactants, used as precursor to the formation of the dispersion ofoleophilic nucleation sites can be any of the surfactants disclosedabove with respect to the hydrocarbon-containing and hydrocarbonstabilizing surfactants. Additional hydrocarbon-containing surfactantsinclude the nonionic and cationic surfactants, including the siloxanesurfactants such as disclosed in U.S. Pat. No. 7,897,682 (Brothers etal.) and U.S. Pat. No. 7,977,438 (Brothers et al.).

The preferred water soluble hydrocarbon-containing compounds are thenucleant surfactants, and the preferred nucleant surfactants are thenonionic surfactants, especially the nonionic hydrocarbon surfactants.Accordingly, in the process of the present invention, when theabove-described nucleation site forming step is used, the nucleantsurfactant is preferably nonionic hydrocarbon surfactant, and thehydrocarbon stabilizing surfactant, whether passivated or unpassivated,is preferably anionic. The nucleant surfactant (andhydrocarbon-containing compound) is also preferably free of aromaticmoiety. Nonionic hydrocarbon-containing surfactants andhydrocarbon-containing compounds containing alkylene oxide units arereadily oxidizable by the polymerization initiator degradation agent.

Nonionic hydrocarbon nucleant surfactants include polyoxyethylene alkylethers, polyoxyethylene alkyl phenyl ethers, polyoxyethylene alkylesters, sorbitan alkyl esters, polyoxyethylene sorbitan alkyl esters,glycerol esters, their derivatives and the like. More specificallyexamples of polyoxyethylene alkyl ethers are polyoxyethylene laurylether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether,polyoxyethylene oleyl ether, polyoxyethylene behenyl ether and the like;examples of polyoxyethylene alkyl phenyl ethers are polyoxyethylenenonyl phenyl ether, polyoxyethylene octyl phenyl ether and the like;examples of polyoxyethylene alkyl esters are polyethylene glycolmonolaurylate, polyethylene glycol monooleate, polyethylene glycolmonostearate and the like; examples of sorbitan alkyl esters arepolyoxyethylene sorbitan monolaurylate, polyoxyethylene sorbitanmonopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylenesorbitan monooleate and the like; examples of polyoxyethylene sorbitanalkyl esters are polyoxyethylene sorbitan monolaurylate, polyoxyethylenesorbitan monopalmitate, polyoxyethylene sorbitan monostearate and thelike; and examples of glycerol esters are glycerol monomyristate,glycerol monostearate, glycerol monooleate and the like. Also examplesof their derivatives are polyoxyethylene alkyl amine, polyoxyethylenealkyl phenyl-formaldehyde condensate, polyoxyethylene alkyl etherphosphate and the like. Particularly preferable are polyoxyethylenealkyl ethers and polyoxyethylene alkyl esters. Examples of such ethersand esters are those that have an HLB value of 10 to 18. Moreparticularly there are polyoxyethylene lauryl ether (EO: 5 to 20. EOstands for an ethylene oxide unit.), polyethylene glycol monostearate(EO: 10 to 55) and polyethylene glycol monooleate (EO: 6 to 10).

Suitable nonionic hydrocarbon nucleant surfactants include octyl phenolethoxylates such as the Triton® X series supplied by Dow ChemicalCompany:

Preferred nonionic hydrocarbon nucleant surfactants are branched alcoholethoxylates such as the Tergitol® 15-S series supplied by Dow ChemicalCompany and branched secondary alcohol ethoxylates such as the Tergitol®TMN series also supplied by Dow Chemical Company:

Ethyleneoxide/propylene oxide copolymers such as the Tergitol® L seriessurfactant supplied by Dow Chemical Company are also useful as nonionicnucleant surfactants in this invention.

Yet another useful group of suitable nonionic hydrocarbon nucleantsurfactants are difunctional block copolymers supplied as Pluronic® Rseries from BASF, such as:

Another group of suitable nonionic hydrocarbon nucleant surfactants aretridecyl alcohol alkoxylates supplied as Iconol® TDA series from BASFCorporation.

Cationic surfactants can also be used as nucleant surfactants. A typicalcationic surfactant has a positively charged hydrophilic portion such asan alkylated ammonium halide, such as alkylated ammonium bromide, and ahydrophobic portion such as a long chain fatty acid

Another group of nucleant surfactants that can be used are thehydrocarbon-containing siloxane surfactants, preferably the hydrocarbonsurfactants wherein the hydrocarbyl groups as described above, areentirely substituted with hydrogen atoms where they could be substitutedby halogen such as fluorine, whereby these siloxane surfactants can alsobe considered as hydrocarbon surfactants, i.e. the monovalentsubstituents on the hydrocarbyl groups are hydrogen. Preferred asnucleant surfactants are the hydrocarbon siloxanes that have nonionicmoieties, i.e., the nonionic hydrocarbon (siloxane) surfactants.

The degradation agent as the oxidizing agent for the nucleant surfactantin the preferred embodiment to form the oleophilic nucleation sites ispreferably a water-soluble free radical polymerization initiator that isalso useful for the polymerization of fluoromonomer. Polymerizationinitiators are not known to be harmful to the polymerization offluoromonomers when used in the proper amount, whereby its introductioninto the aqueous medium to cause the oxidation of the nucleantsurfactant should not cause any problem in the subsequent polymerizationreaction. Moreover, the amount of initiator used as the degradationagent is preferably small, yet effective to result in the desiredoxidation of the hydrocarbon compound/surfactant to form the dispersionof oleophilic nucleation sites. The amount of initiator added to theaqueous polymerization medium is preferably insufficient to causekickoff of the subsequent polymerization reaction. The same is, truewith respect to the amount of initiator remaining in the aqueous mediumafter oxidation of the nucleant surfactant to form the dispersion ofoleophilic nucleation sites This avoids polymerization occurring duringthe initial pressuring up of the polymerization reactor withfluoromonomer, after which kickoff of the polymerization reactionoccurs.

Additional free radical polymerization initiator is added to the aqueousmedium in the pressured-up reactor to provide kickoff of thepolymerization reaction. This would be the second addition ofpolymerization initiator to the aqueous polymerization medium If thedegradation agent is polymerization initiator.

Examples of polymerization initiators that can be used as thedegradation agent in the oleophilic nucleation forming step are thosethat will rapidly oxidize the hydrocarbon-containing compound,preferably nucleant, surfactant at the temperature of the aqueous mediumachievable within the polymerization reactor to form the desiredoleophilic nucleation sites. Rapid reaction is desired so that theresultant oleophilic nucleation sites, now existing in the aqueousmedium that is essentially free of surfactant, can be available for thepolymerization reaction as a dispersion. Preferred initiators for thispurpose are the highly active water-soluble salts of inorganicinitiators such as the inorganic peracids. Preferred initiators are thepersulfate salts, e.g., ammonium persulfate or potassium persulfate.Preferred persulfate initiators are substantially free of metal ions andmost preferably are ammonium salts. Additional initiators useful in thepractice of this invention are water-soluble organic azo compounds suchas azoamidine compounds.

The degradation agent can be the same as or different from thepolymerization initiator used to polymerize the fluoromonomer. When thepolymerization initiator is a mixture of initiators, for example,disuccinic acid peroxide and ammonium persulfate, the degradation agentis considered to be different from the polymerization initiator even ifthe degradation agent were ammonium persulfate

The amount of degradation agent, preferably polymerization initiator,added as the degradation agent to the aqueous medium will depend on themolecular weight of the initiator used that preferably contains theperoxy —O—O— group. Too much initiator used as the degradation agent inthe nucleation site forming step may cause destabilization of thenucleation sites along with premature polymerization of fluoromonomerpressuring up the reactor to kick off, resulting in largerfluoropolymer, fluoroplastic or perfluoroplastic particles being formedin the polymerization step. The amount of initiator is preferably lessthan the amount required to kickoff the polymerization reaction beforeit reaches operating pressure, preferably no greater than 50 ppm, morepreferably no greater than 40 ppm, more preferably no greater than 30ppm, even more preferably no greater than 20 ppm, and most preferably nogreater than about 15 ppm. The minimum amount of initiator added to theaqueous medium can be as little as 1 ppm. The ppm amount of initiatorpresent in the aqueous medium after formation of the dispersion ofnucleation sites will be less than the ppm amounts disclosed herein asbeing added to the aqueous medium by virtue of the oxidation reactioncausing degradation of the initiator. These ppm amounts are based on theweight of water present in the reactor at the time of forming theoleophilic nucleation sites as further described under the EXAMPLES.

A preferred embodiment of forming polymerization sites is wherein theoleophilic nucleation sites are either hydrocarbon-containing orhydrocarbon oleophilic nucleation sites, which are made by addinghydrocarbon-containing surfactant or hydrocarbon surfactant as thenucleant surfactant, each containing hydrophobic moiety and hydrophilicmoiety, to the aqueous polymerization medium and exposing the surfactantto degradation, preferably oxidation, in the aqueous medium to degradethe hydrophilic moiety, thereby enabling the hydrophobic moiety to formthe dispersion of hydrocarbon oleophilic nucleation sites. Thisnucleation site forming step is carried out prior to kickoff of thepolymerization reaction according to the polymerization process of thepresent invention.

Preferably the amount of the nucleant surfactant added to the aqueousmedium is no greater than 50 ppm, and such amount can be any of thelesser amounts mentioned above, selected so as not to be detrimental tothe subsequent polymerization reaction.

Preferably, this degradation is carried out by adding degradation agent,which is preferably oxidizing agent, to the aqueous medium and reactingthe agent with the nucleant surfactant in the aqueous medium, the amountof such agent being insufficient to cause the kickoff of thepolymerizing of the fluoromonomer. Preferably, the degradation agent isalso free radical polymerization initiator and the amount ofdegradation/oxidizing agent or initiator is no greater than 50 ppm.

Preferably, the formation of the dispersion of oleophilic nucleationsites as described above is accompanied by the additional step of addingwater-soluble inorganic salt to the aqueous medium prior to the exposureof the hydrocarbon-containing compound, preferably, nucleant surfactant,to the degradation, preferably oxidation. At the time of thedegradation, preferably oxidation, water-soluble inorganic salt is alsopresent in the aqueous medium to aid the formation of the dispersion ofoleophilic nucleation sites.

The effect of the water-soluble inorganic salt is to either (a) increasethe number of oleophilic nucleation sites, thereby resulting in smallerfluoropolymer, fluoroplastic or perfluoroplastic particles and/or (b)enable the amount of oleophilic nucleation sites formed fromhydrocarbon-containing compound/nucleant surfactant to be reduced for agiven particle size. With respect to (a), this decrease in such particlesize is with respect to a given small amount of compound/nucleantsurfactant present in the degradation, preferably oxidation, reaction.With respect to (b), the desired number of sites can be obtained with asmaller amount of compound/nucleant surfactant to be present in thedegradation, preferably oxidation, reaction, thereby reducing thepossibility for the product of such reaction from inhibiting thesubsequent polymerization reaction. The presence of the ions derivedfrom the salt in aqueous solution provide the beneficial effect.

Examples of water-soluble inorganic salts that can act to aid in thenucleation site forming process include those containing alkali metalcations such as Na and K or NH4⁺ and anions such as —SO₃, —HSO₃, —NO₃ ⁻,—CL⁻, —CO₃ ⁻, —B₄O₇ ⁻, and —HPO₄ ⁻. When the fluoropolymer,fluoroplastic, or perfluoroplastic being made by polymerization is to befabricated by melt extrusion, the salt is preferably an ammonium salt.

The salt is selected such that it is effective to provide the beneficialeffect mentioned above and neither deactivates the degradation agent,preferably initiator, thereby preventing the degradation, preferablyoxidation, reaction from occurring, nor reacts with the initiator toprevent the initiator from reacting with the nucleant surfactant, norinhibits the eventual polymerization. This enables a smaller amount ofhydrocarbon-containing compound, preferably nucleant surfactant, to beused for forming the oleophilic nucleation sites than if no salt wereused. This is especially important in the polymerization process formaking the highest molecular weight perfluoroplastic, PTFE. The salt maybe a reducing agent, but is not necessarily so. The carrying out of thedegradation/oxidation reaction between the nucleant surfactant and thedegradation agent, preferably initiator, in the presence of thewater-soluble inorganic salt includes the possibility that the saltundergoes some transformation, such as a oxidation/reduction reaction,as well. It is apparent that the ionization of the salt in the aqueousmedium has a positive affect on the formation of nucleation sites. Ifthe amount of salt is too large, however, the result can be negative,i.e. a reduced number of nucleation sites and an increased polymerparticle size. The amount of this water-soluble inorganic salt to beadded to the aqueous medium is that which is effective to providebeneficial result. This amount is also small so as not to adverselyeffect the performance of the oleophilic nucleation sites or thesubsequent polymerization reaction. The amount when this conversion ofpositive effect to negative effect depends primarily on the salt, butgenerally this conversion occurs at greater than 125 ppm salt, based onthe weight of water in the reactor at the time of forming the nucleationsites, this basis being further described under EXAMPLES.

Generally to provide benefit to the nucleation site forming process andnot be detrimental either to it or subsequent polymerization of thefluoromonomer in Process 1 and Process 2, the amount of water-solubleinorganic salt present in the aqueous medium at the time of theoxidation reaction, is preferably no greater than 100 ppm, preferably nogreater than 75 ppm, even more preferably no greater than 50 ppm, andmost preferably, no greater than 25 ppm, and preferably when used, atleast 1 ppm, based on the weight of water in the reactor at the time offorming the oleophilic nucleation sites as further described under theEXAMPLES.

In the oleophilic nucleation site-forming process implemented prior topolymerization kickoff, each of these amounts of water solublehydrocarbon-containing compound/nucleant surfactant, water-solubleinorganic salt, and degradation agent, preferably initiator, mentionedabove can be used in any combination of the amounts mentioned. By way ofexample:

-   -   (a) use of no greater than 40 ppm of the compound/nucleant        surfactant can be accompanied by any of the following amounts of        water soluble inorganic salts (no greater than 125 ppm, 100 ppm,        75, ppm, 50 ppm, or 25 ppm), together with any of the following        amounts of degradation agent/initiator (no greater than 50 ppm,        40 ppm, 30 ppm 20 ppm, or 15 ppm);    -   (b) use of no greater than 100 ppm of the water-soluble        inorganic salt can be accompanied by any of the following        amounts of the compound/nucleant surfactant (no greater than 50        ppm, 40 ppm, 30 ppm, or 20 ppm), together with any of the        following amounts of degradation agent/initiator (no greater        than 50 ppm, 40 ppm, 30 ppm 20 ppm, or 15 ppm); and    -   (c) use of no greater than 30 ppm degradation agent/initiator        can be accompanied by any of the following amounts of        compound/nucleant surfactant (no greater than 50 ppm, 40 ppm, 30        ppm, or 20 ppm), together with any of the following amounts of        water-soluble inorganic salt (no greater than 125 ppm, 100 ppm,        75, ppm, 50 ppm, or 25 ppm), etc.

It is also preferred that essentially no reactive fluoromonomer bepresent in the reactor at least at the commencement of the nucleationsite forming step and the concomitant formation of the dispersion ofoleophilic nucleation sites, i.e. the formation of these sites ispreferably in the absence of fluoromonomer that may preferentially reactwith the small amount of degradation agent/initiator used as thedegradation, preferably oxidizing, agent.

In a typical process for forming the dispersion of oleophilic nucleationsites, the reactor is charged with deionized and deaerated water. Theoleophilic nucleation sites can conveniently be formed in-situ withinthis aqueous medium charged to the reactor by addinghydrocarbon-containing compound, preferably nucleant surfactant, to theaqueous charge in the small amount desired. Preferably, water-solubleinorganic salt is also added to this aqueous charge and these twocompounds are mixed together. The hydrocarbon-containingcompound/nucleant surfactant can conveniently be converted to theoleophilic nucleation sites by degradation, preferably oxidizing, thecompound/nucleant surfactant in the aqueous medium in the reactor and inthe presence of the water-soluble salt. The degradation agent canconveniently be the small amount of water-soluble polymerizationinitiator added to the aqueous medium. The temperature of the aqueousmedium will be at the temperature effective to cause the degradationreaction, which is preferably an oxidizing reaction, to occur and willgenerally be from 25 to 120° C., preferably 40 to 120° C., morepreferably from 50 to 120° C., even more preferably 60 to 120° C., andmost preferably from 70 to 120° C., and this temperature can be the sameor similar temperature at which the subsequent polymerization is carriedout. The temperature used will primarily depend on the temperaturedesired for the later polymerization step, which temperature will alsobe high enough for the degradation agent/initiator to become reactive.The degradation, preferably oxidation, reaction is carried outsufficiently to degrade the hydrophilic moiety of the nucleantsurfactant to enable the residue of the oxidized compound to becomeoleophilic nucleation sites. The oleophilic nucleation sites althougholeophilic are invisible in the aqueous medium. The formation of thedispersion of nucleation sites commences with the start of thedegradation, preferably oxidation reaction. It is contemplated that thisreaction may continue as the reactor is pressured up with fluoromonomeradded to the reactor to achieve the reactor pressure desired forkickoff. Thereafter, the polymerization step of the process of thepresent invention is carried out, comprising pressuring up the reactorwith the fluoromonomer to be polymerized, followed by initiatorinitiated kickoff of the polymerization reaction essentially in theabsence of water soluble hydrocarbon-containing compound, includinghydrocarbon-containing surfactant, and delayed addition ofhydrocarbon-containing, preferably hydrocarbon, stabilizing surfactant,and metering of the this surfactant into the aqueous medium during thesubsequent polymerization reaction at the rates and time of injectionmentioned above.

EXAMPLES

The following surfactants are used in the Examples. When used to formpolymerization sites that are oleophilic nucleation sites, thesesurfactants are referred to in the Examples as nucleants or nucleantsurfactants.

The Pluronic® 31R1 is nonionic and has the structure shown above,wherein both ends of the surfactant are hydrophobic and the center ishydrophilic.

Avanel® S-70 is an anionic surfactant containing ethylene oxide groupsand having the structure shown above;

Silwet® L7600 is a nonionic pendant-type polyethyleneoxide-modifiedpolydimethylesiloxane available from GE Silicones.

Tergitol® 100 is a 70/30 wt % blend of TMN 6/TMN 10 identified earlierherein as members of the Tergitol® TMN series of surfactants, which arebranched nonionic surfactants having the structure shown above

CTMAB is cetyltrimethylammonium bromide (CH₃(CH₂)₁₅N(CH₃)₃Br), acationic surfactant.

SDS is sodium dodecyl sulfate, a linear anionic hydrocarbon surfactantwith no ethylene oxide groups.

SOS is sodium octyl sulfonate

Triton® X-100 is a nonionic surfactant, which is octyl phenol polyethoxyalcohol having the structure shown above.

The wax used in the Examples is a paraffin wax.

Fluoropolymer, fluoroplastic, and perfluoroplastic particle sizes are ofthe raw dispersion of polymer particles as measured using laser lightscattering with a Zetasizer Nano-ZS manufactured by Malvern Instruments.Samples for analysis are prepared in 10×10×45 mm polystyrene cuvettes,capped and placed in the device for analysis. Preparation of the sampleis as follows. Water used to flush the cuvette and used to dilute thedispersion sample is rendered substantially free of particles by drawingdeionized, deaerated water into a 10 cc glass hypodermic syringe withlocking tip. A Whatman® 0.02 micron filter (Cat. No. 6809-2002) isfitted to the locking tip of the syringe and pressure is applied forcewater through the filter and into the cuvette. Approximately 1.5 ml ofwater is placed in the cuvette, the cuvette is capped, shaken anduncapped. Water is poured out of the cuvette thus assuring the cuvetteis free of polymer. Approximately 2.5 gm of filtered water is placed inthe cuvette. One drop of the polymer particle dispersion to be analyzedis added to the cuvette. The cuvette is capped and shaken to completelymix the fluoropolymer particles in the water. The sample is placed inthe Nano-ZS for determination of Dv(50). Dv(50) is the median particlesize based on volumetric particle size distribution, i.e. the particlesize below which 50% of the volume of the population resides.

Melt flow rate (MFR) is determined using the procedure of ASTM D 1228and melt temperature and plastometer piston weight conditions that arestandard for the polymer as indicated in the ASTM procedure for theparticular polymer.

Melting temperature is measured by Differential Scanning calorimeter(DSC) according to the procedure of ASTM D 4591. The PTFE DSC meltingtemperature is obtained from the first time the polymer is heated abovethe melting temperature, also referred to as the first heat, inaccordance with ASTM D-4591-87. The melting temperature reported is thepeak temperature of the endotherm on first melting.

The term nucleant used herein refers to the surfactant from which theoleophilic nucleation sites are obtained by degradation, preferablyoxidation, of the surfactant in an aqueous medium.

Unless otherwise indicated, the definition (calculation) of ppm hereinis the weight of the ingredient divided by the weight of water presentin the reactor at the time of the event when the concentration in ppm isbeing determined. Ppm of water soluble hydrocarbon-containingcompound/nucleant surfactant, salt, if any, and degradationagent/initiator in the precharge composition described above and in theExamples is based on the weight of water initially charged to thereactor and any additional water charged containing each of thecompound/nucleant surfactant, salt, if present, and degradationagent/initiator ingredients. Thus, the amount of water present in thereactor at the time of forming the oleophilic nucleation sites is theweight of water on which the ppm of the compound/nucleant surfactant,salt, if any, and degradation agent/initiator is determined. This amountwill not include water added as solvent for the initiator added to theaqueous medium to provide for kickoff of the polymerization reaction orfor addition of stabilizing surfactant to the aqueous medium. Thisamount of added water would be included in the ppm calculation of anysurfactant present in the aqueous medium at the time of polymerizationkickoff. For simplicity, when the water added contains a dissolvedingredient, such as compound/nucleant surfactant, salt, degradationagent/initiator, the resultant solution is considered to be entirely ofwater for purposes of ppm calculation. An exception to this way ofdetermining ppm is the determination of the concentration of stabilizingsurfactant based on the total weight of fluoropolymer, fluoroplastic, orperfluoroplastic particles present in the dispersion upon completion ofthe polymerization reaction, as described in EXAMPLE 10.

The disclosure of numerical amounts as “no greater than” and the likeherein has the same meaning as the same numerical amounts beingdesignated as being particular amounts or less. Thus, no greater than 50ppm has the same meaning as 50 ppm or less. Similarly, the disclosure ofnumerical amounts of “at least” and the like herein has the same meaningas the same numerical amounts being designated as being particularamounts or greater. Thus, at least 45 wt % has the same meaning as 45 wt% or greater.

The reactor pressures disclosed herein are absolute pressures unlessotherwise indicated as being gauge pressures (psig). The MPa and KPapressures disclosed as corresponding to the psig gauge pressures areabsolute pressures.

Batch time is the polymerization time from kickoff until completion ofthe polymerization reaction.

Wt % coagulum is calculated by the following formula: wt % coagulum=[wtof coagulum/total polymer produced]×100. Total polymer produced is thecombined weight of the coagulum and the dispersed fluoropolymerparticles. All weights are measure of dry polymer.

Example 1

This Example contains experiments of polymerization with delayedaddition of the hydrocarbon surfactant and its metering into thepolymerization reactor and improvements obtained when the kickoff of thepolymerization reaction is preceded by the formation of a dispersion ofoleophilic nucleation sites, with and without the presence of salt.

General procedure for polymerization with no nucleation site formationstep prior to polymerization kickoff: To a 12 liter, horizontallydisposed, jacketed, stainless steel reactor with a two blade agitator isadded 5700 gm of deionized, deaerated water and 250 gm of liquid wax.The reactor is sealed and placed under vacuum. The reactor pressure israised to 30 psig (310 kPa) with nitrogen and brought to vacuum 3 times.Reactor agitator is set at 65 RPM. The reactor is heated to 90° C. andTFE is charged to the reactor to bring the reactor pressure to 400 psig(2.86 MPa). At time zero, 150 ml of initiator solution of deionized,deaerated water containing 0.05 gm of ammonium persulfate (APS) and 3.5gm of disuccinic acid peroxide (DSP) is injected at 80 ml/min. Kickofftime (“KO Time” in Table A) is measured as the time (since time zero)necessary to drop 10 psi (69 kPa) from the maximum pressure observedduring injection of the charge initiator solution. At kickoff, reactorpressure is brought back to 400 psig (2.86 MPa) with TFE and maintainedat that pressure for the duration of the polymerization. After 100 gm ofTFE is fed since kickoff, a stabilizer surfactant solution is pumped tothe reactor at the rate of 4 ml/min, which corresponds to a surfactantmetering rate of 0.28 g/l-hr. This delay in commencing the surfactantaddition to the aqueous medium corresponds to a PTFE concentration inthe aqueous medium of 1.68 wt % before this addition begins(calculation: 100 gm TFE÷[100+5700+150]×100). Preparation of thestabilizer solution is given below. After 750 gm of TFE has been addedto the reactor since kickoff, the Batch Time (Table A) is recorded, theagitator is stopped, the reactor is vented to atmospheric pressure andthe dispersion is discharged. Upon cooling, wax is separated from thedispersion. The PTFE dispersion has a pH of 2.8, % solids of 11.75 andDv(50) of 198 nanometers (Experiment A-1 in Table A). The PTFE has ahigh molecular weight as indicated by DSC melting temperature of 332° C.(1st heating) and DSC heats of fusion of 76 J/g (1^(st) heating) vs.47.5 J/g (2^(nd) heating), reflecting the extremely high melt viscosityof the PTFE reducing ability of the PTFE to recrystallize upon coolingafter first heating.

The surfactant in the surfactant stabilizing solution used in the aboveprocedure is passivated by the following procedure: In a 1 liter,jacketed round bottom flask is added 681.74 gm of deionized, deaeratedwater, 10.5 gm of sodium dodecyl sulfate (ACS Reagent, >99.0%) and 0.315gm of Iron(II) sulfate heptahydrate. The contents are agitated until allsolids are dissolved. The solution pH is adjusted to 2.0-2.5 with 12 to14 drops of concentrated sulfuric acid. 37.34 gm of 30 wt % hydrogenperoxide aqueous solution is slowly added to the agitating mixture.Agitation continues for 1 hr at room temperature (22-23° C.) after whichtime the resultant oxidized surfactant in aqueous solution is used inthe above polymerization procedure.

The above polymerization procedure has no nucleation step prior topolymerization kickoff, and the polymerization result is reported as A-1in Table A.

The nucleation step is practiced by repeating the above polymerizationprocedure except that 5200 gm of deionized, deaerated water and 250 gmof liquid wax is the initial charge to the reactor. Then, 500 gm ofdeionized, deaerated water containing 0.085 gm of surfactant (Nucleant,Table A) and 0.4 gm of sodium sulfite water-soluble inorganic salt isadded to the reactor. After heating the reactor to polymerizationtemperature but before charging TFE to bring the reactor to operatingpressure, 50 ml of an aqueous solution containing 0.5 gm of APS perliter of deionized, deaerated water is added. The APS is the degradationagent for the oxidation of the nucleant surfactant. The surfactantconcentration is 14.8 ppm (calculation: [0.085÷5750]×10⁶), the saltconcentration is 70 ppm, and the initiator concentration is 4.3 ppm.Under the conditions/additives present in the aqueous medium (prechargecomposition), the APS causes an oxidation reaction of the hydrocarbonsurfactant to occur, resulting in the formation of oleophilic nucleationsites dispersed in the aqueous medium. The presence of these sites isindicated by the smaller particle size (Dv(50) of the PTFE particlesreported in Table A for Experiments A-3 through A-9, using nonionic,anionic, and cationic surfactants. The long time to polymerizationkickoff for Experiment A-9 is attributed to the aromatic moiety presentin this surfactant, the other surfactants used being non-aromatic, i.e.free of aromatic moiety. It is contemplated that this kickoff time canbe reduced by reducing the amount of this surfactant used. The delay inthis repeat experiment reported as Experiments A-3 to A-9 in Table A is1.67 wt % fluoropolymer concentration before the stabilizing surfactantaddition begins (calculation: 100 g TFE÷[100+5200+500+50+150]×100). Theactual time of delay for all the experiments reported in Table A rangefrom 4.4 to 6 min. after kickoff before the stabilizing surfactantaddition begins.

Experiment A-2 is the result of the polymerization procedure describedabove in which no nucleant surfactant is present, except that the sodiumsulfite salt is added in the amount shown in Table A. The presence ofthe salt and no nucleant surfactant results in a much larger PTFEparticle size indicating that the salt is causing fewer polymerparticles to be formed during the initial stage of polymerization.

TABLE A Batch Na₂ KO Time Polymer Exp. Nucleant SO₃ Time “B” SolidsDv(50)* Particles Made # Name ppm min min % nm Number gm A-1 4.3 37.911.75 198 (311) 9.44E+16 829 A-2 70 2.4 45.4 12.06 358 (556) 1.64E+16853 A-3 Pluronic ® 70 3.4 36 11.97 113 (176) 5.20E+17 849 31R1 A-4Avanel ® S70 70 4.4 34.1 12.04 119 (184) 4.51E+17 859 A-5 Silwet ® L760070 2.8 30.1 11.97 130 (202) 3.43E+17 852 A-6 Avanel ® S74 70 3.4 33.212.18 134 (207) 3.21E+17 874 A-7 Tergitol ® 100 70 4.8 33.1 11.85 136(213) 2.94E+17 837 A-8 CTMAB 70 3 36.8 11.84 160 (251) 1.80E+17 833 A-9Triton ® X-100 70 20.9 44.4 11.82 154 (241) 2.03E+17 838 *The Dv(50)values in parentheses are extrapolated from the measured Dv(50) value(no parentheses) using the equation presented below.

The above polymerizations are conducted as a screening series ofpolymerizations, i.e. carried out to dispersion PTFE solids (particles)content of about 11-13 wt %, based on total weight of the dispersion,resulting from the feed of just 750 gm of TFE after kickoff to thereactor for the polymerization reaction. The screening result availablefrom the above polymerizations can be extrapolated to the polymerizationresult if the polymerization were extended to consume 3200 g of TFE toproduce a dispersion solids content of about 34 wt %. This extrapolatedresult is reported in Table A as the Dv(50) in parenthesis Thisextrapolation can be done by using the following equation:D2=[P2×(D1)³ /P1]^(1/3)wherein P1 is the actual amount of polymer produced (in grams) havingthe Dv(50) particle size D1 (in nanometers); P2 equals the projectedpolymer produced in grams, and D2 is the projected particle size (innanometers) of the P2 polymer. Sample calculation for Experiment A-3:D2=(3200×113×113×113/849)^(1/3)=(5438481.04)^(1/3)=176

Experiment A-1 uses delayed addition of the surfactant and its meteringas the polymerization reaction proceeds. Neither nucleant surfactant norsalt is used, i.e. the nucleation step procedure described above is notused. Experiment A-2 shows the disadvantage in just using the saltaddition, without formation of nucleation sites, i.e. no nucleantsurfactant is used. Experiment A-2 obtains a poorer result as a muchlarger Dv(50) particle size, much larger than for Experiment A-1.Comparison of the Dv(50) results of Experiment A-1 with Experiments A-3to A-10 reveals the effect of the oleophilic nucleation sites present inExperiments A-3 to A-10 on providing a smaller fluoropolymer particlesize. The batch time for experiment A-1 is comparable to the batch timesfor Experiments A-3 to A10, indicating that delayed addition of thestabilizing surfactant to the aqueous medium together with metering ofsubsequent additions of the surfactant to the aqueous medium iseffective to reduce telogenicity of the hydrocarbon surfactant.

The above polymerization procedure is repeated in a series ofexperiments in which the nucleation step is included in thepolymerization procedure along with varying the inorganic salt(Experiments B-1 to B-3), except that no salt is present in thenucleation site forming step in Experiment B-4. The nucleant surfactantis 14.8 ppm Pluronic® 31R1. The amount of salt adjuvant is 70 ppm andthe amount of APS initiator is 4.3 ppm. The delay in commencing thestabilizing surfactant addition is 1.67 wt % PTFE concentration in theaqueous medium. The results are reported in Table B.

TABLE B Batch Dispersion Polymer Exp. Salt Time solids Dv(50) ParticlesMade # Name min % nm Number gm B-1 Na₂SO₃ 33.1 11.81 118 4.404E+17 818B-2 NaHSO₃ 38.3 11.72 95.1 8.487E+17 826 B-3 Na₂S₂O₅ 40.3 11.92 1076.016E+17 833 B-4 — 36.0 11.68 125 3.81E+17 842

As shown in Table B, different salts all provide small PTFE particlesizes. Experiment A-4 shows the Dv(50) result when nucleant surfactant,but no salt is used.

The PTFE made in all these polymerizations exhibits the characteristicsdescribed earlier in this Example.

Example 2

This Example provides the preparation of modified PTFE.

To a 12 liter, horizontally disposed, jacketed, stainless steel reactorwith a two blade agitator is added 5200 gm of deionized, deaerated waterand 250 gm of liquid wax. To the reactor is added an additional 500 gmof deionized, deaerated water which contains 0.02 gm of Pluronic® 31R1and 0.4 gm of sodium sulfite. The reactor is sealed and placed undervacuum. The reactor pressure is raised to 30 psig (310 kPa) withnitrogen and vented to atmospheric pressure. The reactor is pressuredwith nitrogen and vented 2 more times. The agitator speed is set to 65RPM and the reactor is heated to 90° C. 40 ml of initiator solutioncontaining 0.5 gm of ammonium persulfate (APS) per liter of water isadded to the reactor. This is the precharge composition. Theconcentrations of Pluronic surfactant, salt and initiator are 3.4 ppm,69.6 ppm, and 3.5 ppm, respectively.

The reactor is pressured up by charging the reactor with 12.0 gm ofhexafluoropropylene (HFP) and 650 gm of TFE to bring the reactorpressure to 400 psig (2.86 MPa). At time zero, 150 ml of an initiatorsolution composed of 11.67 gm of disuccinic acid peroxide solution (70wt % DSP), 0.17 gm of ammonium persulfate and 488.3 gm of deionized,deaerated water is charged to the reactor at 80 ml/min. After 2.0minutes from the start of initiator injection the reactor pressure drops10 psi (69 kPa) from the maximum pressure observed during injection ofthe initiator solution. Reactor pressure is brought back to 400 psig(2.86 MPa) with TFE and maintained at that pressure for the duration ofthe polymerization. After 100 gm of TFE has been fed since kickoff,stabilizing surfactant solution (preparation described below) is pumpedto the reactor at a rate of 4 ml/min (0.28 g/l-hr) until the end of therun. This delay in commencing the surfactant addition to the aqueousmedium corresponds to 1.67 wt % concentration of modified PTFE in theaqueous medium. After 155.6 minutes since kickoff, 3100 gm of TFE and688 ml of stabilizing surfactant solution has been added to the reactor.The agitator is stopped, the reactor is vented to atmospheric pressureand the dispersion is discharged. Upon cooling, liquid wax is separatedfrom the dispersion and the dispersion is filtered to remove undispersedsolids (coagulum). The reactor is opened and all coagulum is removedfrom the reactor. Reactor cleanout is combined with the filtered solidsand dried in a vacuum oven. To get a measure of coagulum (totalundispersed solids), liquid wax adhering to this polymer is furtherremoved by centrifuging and blotting the polymer. Total coagulum is thusdetermined to be 120.4 gm. Total recovered liquid wax is 208.7 gm. Thedispersed fluoropolymer particles constitute 32.8 wt % of the aqueousmedium containing this dispersion. The dispersed particles have anaverage particle size by volume, Dv(50), of 255 nm. These particles arecoagulated by diluting the dispersion to about 10 wt % solids and addingaqueous ammonium carbonate solution followed by vigorous agitation untilthe polymer particles fully separate from the water. The polymer isdried in a vacuum oven at 110° C. for 12 hours. Melting point of thispolymer as measured by DSC on first heat is 335° C. Compositionalanalysis by FTIR gives 0.5 wt % HFP. This modified PTFE has a molecularweight (Mn) exceeding 10⁶ and a melt creep viscosity exceeding 10⁶ Pa·s.

The stabilizing surfactant solution is prepared as follows: In a 1liter, jacketed round bottom flask is added 492.5 gm of deionized,deaerated water, 7.5 gm of sodium dodecyl sulfate (ACS Reagent, >99.0%)and 0.225 gm of Fe(⁺²) sulfate heptahydrate. The contents are agitateduntil all solids are dissolved. The solution pH is adjusted to 3.22 withtwo drops of concentrated Sulfuric Acid. 18.75 gm of 30 wt % hydrogenperoxide is added to the mixture. The mixture is heated to 40° C. whilestirring and held at temperature for 2 hours. The solution is dischargedand cooled in an ice bath to rapidly bring the fluid to ambienttemperature. The final mixture has a pH of 2.76.

Example 3

This Example provides the preparation of PFA.

To a 12 liter, horizontally disposed, jacketed, stainless steel reactorwith a two blade agitator is added 7500 gm of deionized, deaeratedwater. To the reactor is added an additional 500 gm of deionized,deaerated water which contains 0.025 gm of Pluronic® 31R1 and 0.2 gm ofsodium sulfite. The reactor is sealed and placed under vacuum. Thereactor pressure is raised to 30 psig (310 kPa) with nitrogen andevacuated three times. Agitation is begun and the agitator speed is setto 70 RPM. 100 ml of PPVE and 0.1 gm of ethane is added to the reactor.15 ml of initiator solution containing 6.2 gm ammonium persulfate perliter of deionized deaerated water is added to the reactor. Theconcentrations of surfactant, salt and initiator are 3.1 ppm, 25 ppm and11.6 ppm, respectively. The reactor is heated to 85° C. and then TFE(approximately 290 gm) is charged to the reactor to bring the reactorpressure to 300 psig (2.17, MPa). At time zero, 100 ml of initiatorsolution is charged to the reactor at 80 ml/min and then the initiatoris pumped continuously at 0.6 ml/min until the end of the run. Kickoffoccurs after 1.5 minutes from the start of initiator injection when thereactor pressure drops 10 psi (69 kPa) from the maximum pressureobserved during injection of the initiator solution. At kickoff, thereactor temperature controller setpoint is reduced from 85° C. to 75° C.Reactor pressure is controlled at 300 psig (2.17 MPa) with addition ofTFE and 0.03 ml PPVE per gram of TFE fed for the duration of thepolymerization. After 1000 gm of TFE has been fed since kickoff, asurfactant solution in deionized, deaerated water containing 0.5 gm ofsodium dodecyl sulfate (SDS) per 100 g of deionized, deaerated water asthe stabilizing surfactant is pumped into the reactor at a rate of 1ml/min until the end of the run. This delay in commencing the additionof stabilizing surfactant to the aqueous medium corresponds to 11.6 wt %concentration of PFA in the aqueous medium as calculated below. The timedelay is 50 min. The metering rate of the stabilizing surfactant is0.025 g/l-hr. After 135 minutes since kickoff, 2300 gm of TFE and 86 mlof surfactant solution have been added to the reactor. The agitator isstopped, the reactor is vented to atmospheric pressure and thedispersion is discharged. 10.68 kg of PFA aqueous dispersion is producedwith 22.1 wt % solids content in the aqueous medium and 114 nm rawdispersion particle size. Coagulum obtained from filtering thedispersion through cheesecloth and from cleaning the reactor is dried ina vacuum oven and measures 63 gm (0.6 wt %). PFA Polymer is isolated byfreezing a dispersion sample followed by thawing, filtration, washingand drying. The polymer contains 6.0 wt % PPVE as measured by FTIR andhas a MFR of 10.8 gm/10 min.

Calculation of wt % (fluoropolymer) conc. in aqueous medium:

A = total  weight  of  polymer  producedB = total  weight  of  water  in  reactorA = wt  T F E  fed/(1-weight  fraction  of      P P V E  in  fluoropolymer)A = 1000/(1-0.06) = 1063.8B = total  weight  of  water  added  to  reactorB = 7500 + 500 + 15 + 100 + (0.6 × 50) = 8145 $\begin{matrix}{{{Wt}\mspace{14mu}\%\mspace{14mu}{concentration}} = {\left\lbrack {A/\left( {A + B} \right)} \right\rbrack \times 100}} \\{= {\left\lbrack {1063.8/\left( {1063.8 + 8145} \right)} \right\rbrack \times 100}} \\{= 11.6}\end{matrix}$

This experiment is repeated except for the following: Rather than adding15 ml of initiator solution before heating the reactor to 85° C., theinitiator solution is added after heating the reactor and before TFE ischarged in order to bring the reactor to 300 psig (2.17 MPa). Kickofftime is 2.6 minutes, batch time is 138 minutes and 89 ml of surfactantsolution is added to the reactor. 10.52 kg of aqueous dispersion isproduced with 22.0 wt % solids content and 128 nm raw dispersionparticle size. Coagulum obtained from filtering the dispersion throughcheesecloth and from cleaning the reactor is dried in a vacuum oven andmeasures 95 gm. The isolated polymer contains 5.4 wt % PPVE as measuredby FTIR and has a MFR of 12.0 gm/10 min. The delay in commencing theaddition of the stabilizing surfactant to the aqueous medium is 49.5 minand corresponds to a PFA concentration of 11.5 wt %.

Example 4

The Example provides the preparation of FEP.

To a 12 liter, horizontally disposed, jacketed, stainless steel reactorwith a two blade agitator is added 6000 gm of deionized, deaeratedwater. To the reactor is added an additional 500 gm of deionized,deaerated water which contains 0.015 gm of Pluronic® 31R1 and 0.1 gm ofsodium sulfite. The reactor is sealed and placed under vacuum. Thereactor pressure is raised to 30 psig (310 kPa) with nitrogen andevacuated three times. Agitation is begun and the agitator speed is setto 75 RPM. The reactor is heated to 95° C. 2.6 ml of initiator solutioncontaining 22 gm ammonium persulfate per liter of deionized, deaeratedwater is added to the reactor. The concentrations of surfactant, saltand initiator are 2.3 ppm, 15.4 ppm, and 8.8 ppm, respectively.

HFP and TFE are charged to the reactor in a weight ratio of 1.857/1HFP/TFE in order to bring the reactor pressure to 435 psig (3.10 MPa).At time zero, 30 ml of the above initiator solution is charged to thereactor at 80 ml/min and then the initiator is continuously pumped at1.5 ml/min until the end of the run. Kickoff occurs after 3.5 minutesfrom the start of initiator injection when the reactor pressure drops to425 psig (3.03 MPa). For the duration of the run, reactor pressure iscontrolled at 425 psig (3.03 MPa) with addition of TFE. After 300 gm ofTFE has been fed since kickoff, a surfactant solution containing 1.45 gmof passivated sodium dodecyl sulfate per 100 gm of solution is pumped tothe reactor at a rate of 0.75 ml/min until the end of the run. The delayin commencing the addition of stabilizing surfactant to the aqueousmedium is 37.5 min and corresponds to an FEP concentration in theaqueous medium of 4.9 wt %. The metering rate of the surfactant into theaqueous medium is 0.054 g/1-hr. The passivation treatment of thestabilizing surfactant (SDS) is the same as set forth in Example 1.After 248 minutes since kickoff, 2000 gm of TFE and 158 ml of surfactantsolution has been added to the reactor. The agitator is stopped, thereactor is vented to atmospheric pressure and the dispersion isdischarged. 8.70 kg of aqueous dispersion is produced with 23.2 wt %solids content and 165 nm raw dispersion particle size. Coagulumobtained from filtering the dispersion through cheesecloth and fromcleaning the reactor is dried in a vacuum oven and measures 270 gm.Polymer is isolated by freezing a dispersion sample followed by thawing,filtration, washing and drying. The polymer contains 10.6 wt % HFP asmeasured by FTIR and has a melting point of 273° C.

Example 5

This Example compares polymerization results for preparing PTFE havingthe characteristics of the PTFE of Example 1 by using different delaysafter polymerization kickoff, for introducing the stabilizing surfactantinto the aqueous polymerization medium.

A summary of the polymerization conditions is as follows: 5700 gm ofdeionized, deaerated water is charged to the reactor with 0.085 gm ofPluronic® 31R1, 0.02 gm of Triton X-100 and 0.4 gm of Na₂SO₃ and heatedto 90° C. Then, 80 ml (0.04 gm APS) is added to the aqueous medium. Theconcentrations of surfactants are in the aqueous medium 14.7 ppm and 3.4ppm, respectively, and the concentration of salt is 69 ppm and of theinitiator is 6.9 ppm. The reactor is pressured to 400 psig (2.86 MPa)with the addition of 660 gm of TFE. For initiating the polymerization,150 ml of an initiator solution containing 0.33 gm APS and 22.33 g (70%active DSP) per liter of deionized, deaerated water is added to thereactor. After kickoff (KO) the pressure is maintained at 2.86 MPa withthe addition of TFE. At 22 gm TFE feed (Experiments C-3 and C-4) or 300gm TFE feed (Experiments C-1 and C-2, the introduction of the SDS or SOSstabilizing surfactants into the aqueous polymerization medium is begun.The delay of 22 gm of TFE being consumed before surfactant addition iscommenced corresponds to a PTFE concentration in the aqueous medium of0.37 wt %. The delay of 300 gm of TFE being consumed before surfactantaddition is commenced corresponds to a PTFE concentration in the aqueousmedium of 5.06 wt %. Stabilizer surfactant solution is pumped into theaqueous medium at a rate of 2 ml/min until 1000 gm of TFE feed. Thispumping rate is a metering rate of 0.14 g/l-hr. Then, the pump rate israised to 3 ml/min (0.22 g/l-hr). The concentration of SDS or SOS in thepump solution is 1.445 gm per 100 gm of fluid.

TABLE C Start Stop Batch % Stabilizer Stabilizer Stabilizer Time Dv(50)solids Exp. ppm Type gm TFE Fed min nm % C-1 898 SDS 300 2200 166 235 26C-2 1327 SOS 300 1760 464 196 2 C-3 1327 SDS 22 968 464 146 18 C-4 1327SOS 22 1348 464 174 23The results shown in this Table is that the delay of 22 gm (0.37 wt %)is too short for both SDS and SOS, as indicated by the longpolymerization time of 464 min. This delay of 22 gm of TFE consumedbefore surfactant addition is commenced is the similar to the 0.36 wt %delay practiced in Example 1 of U.S. Pat. No. 7,521,513 making VF₂/HFPcopolymer (calculation: [90÷(25000+100+90)×100]. Upon reaching the batchtime of 464 min, the polymerization reaction is stopped, without the TFEmonomer feed ever reaching the 2200 gm PTFE goal. Experiment C-1provides the best result, enabling the 2200 gm goal to be met in a muchshorter batch time than Experiments C-2 through C-4.

The above polymerizations are repeated with the following changes: theinitiator pump rate is faster (4.0 ml/min.), and the delay in stabilizersurfactant feed is until 100 gm of TFE makeup feed to the reactor afterkickoff. This delay corresponds to a PTFE concentration in the aqueousmedium of 1.66 wt %. These changes in the repetition of thepolymerizations are undertaken in recognition of the benefit (reducedtelogenicity) of the stabilizing surfactant being passivated asdescribed below. Pumping continues to the end of the run. The resultsare shown in Table D.

The SDS and SOS stabilizing surfactants are passivated prior tointroduction into the aqueous polymerization medium according to thefollowing procedure:

Into a 1 L glass bottle, 10.5 gm of sodium dodecyl sulfate is added to681.74 gm of deaerated water and further stirred using stir bar untilall solids are dissolved and the solution is clear. 0.315 gm of iron(⁺²) sulfate heptahydrate is added to this solution at room temperature.The pH is then adjusted to 2.0-2.5 with 12-14 drops of conc. H₂SO₄. Thecontents of this bottle are transferred to a 3-necked 1 L glass reactorthat has a heating/cooling jacket equipped with thermometer and anoverhead stirrer. 37.34 gm of H₂O₂ (30% solution) are then added slowlyto this stirred solution. The solution is then further stirred at roomtemperature for 60 additional minutes after completion of the H₂O₂addition. The solution containing the resultant passivated SDS reactionis then discharged into 1 L glass bottle, and this is the solution usedfor pumping stabilizing surfactant into the polymerization reaction. Thesame passivation procedure is used for SOS, except that it is added tothe IL glass bottle as a solution in water, available as Witconate®NAS-8 surfactant, to provide the same 10.5 gm of SOS.

TABLE D Start Stabilizer TFE Batch % Stabilizer gm TFE Makeup TimeDv(50) solids Example ppm Type Feed gm min nm % D-1 922 SDS 100 3100 110188 34 D-2 1127 SOS 100 3100 134 194 16The passivation of the SDS and SOS stabilizing surfactants results inmuch shorter batch times to make a greater amount of PTFE.

Example 6

The Example compares polymerization results from stabilizing surfactantpassivated at different temperatures. The passivation procedure is asfollows: In a 1 liter, jacketed round bottom flask is added 681.74 gm ofdeionized, deaerated water, 10.5 gm of sodium dodecyl sulfate (ACSReagent, >99.0%) and 0.315 gm of Fe(⁺²) sulfate heptahydrate. Thecontents are agitated until all solids are dissolved. The solution pH isadjusted to 2.0-2.5 with 12-18 drops of concentrated sulfuric acid.While holding the mixture at the desired passivating temperature asshown for Experiments F-1, F-2, and F-3 in Table F by circulatingthermally regulated water through the flask jacket, 37.34 gm of 30 wt %hydrogen peroxide is added to the mixture. The mixture is agitated for 1hour before being discharged and as necessary rapidly cooled to roomtemperature using an ice bath.

The polymerization procedure is as follows: To a 12 liter, horizontallydisposed, jacketed, stainless steel reactor with a two-blade agitator isadded 5200 gm of deionized, deaerated water and 250 gm of liquid wax. Tothe reactor is added an additional 500 gm of deionized, deaerated waterwhich contains 0.085 gm of Pluronic® 31R1, 0.02 gm of Triton® X-100 and0.4 gm of sodium sulfite. The reactor is sealed and placed under vacuum.The reactor pressure is raised to 30 psig (310 kPa) with nitrogen andbrought to vacuum 3 times. The agitator speed is set to 65 RPM and thereactor is heated to 90° C. 0.04 g APS initiator is next charged to theheated aqueous medium (80 ml of 0.5 g/l initiator solution in deionized,deaerated water) to provide an APS concentration in the precharge of 6.9ppm. The surfactant concentrations are 14.7 ppm and 3.5 ppm,respectively, and the salt concentration is 70 ppm in the aqueousmedium. TFE is charged to the reactor to bring the reactor pressure to400 psig (2.86 MPa). At time zero, 150 ml of an initiator solutioncomposed of 11.67 gm of (70% active) disuccinic acid peroxide, 0.17 gmof ammonium persulfate (APS) and 488.3 gm of deionized, deaerated wateris charged to the reactor at 80 ml/min. Approximately 7 minutes from thestart of initiator injection the reactor pressure drops 10 psi (69 kPa)from the maximum pressure observed during injection of the initiatorsolution. Reactor pressure is brought back to 400 psig (2.86 MPa) withmakeup TFE and maintained at that pressure for the duration of thepolymerization by continuous addition of makeup TFE. After 100 gm of TFEhas been fed since kickoff, surfactant solution is pumped to the reactorat a rate of 4 ml/min until the end of the run. This delay in commencingaddition of the stabilizing surfactant to the aqueous medium correspondsto a PTFE concentration in the aqueous medium of 1.66 wt %, and themetering rate of the surfactant into the aqueous medium is 0.29 g/l-hr.The batch time (time from kickoff to the end of makeup TFE addition) isshown in the table below. After 3100 gm of makeup TFE has been added tothe reactor, the agitator is stopped, the reactor is vented toatmospheric pressure and the dispersion is discharged. Upon cooling,liquid wax is separated from the dispersion and the dispersion isfiltered to remove undispersed solids. The reactor is opened and alladhered polymer removed from the reactor. Reactor cleanout is combinedwith the filtered solids and dried in a vacuum oven. To get a measure ofcoagulum (total undispersed solids) liquid wax adhering to this polymeris further removed by centrifuging and blotting the polymer. Coagulumthus obtained in these examples is 35-38 grams. Aqueous dispersionproduced is 9.7 kg with 34% solids and an average particle size byvolume, Dv(50), as shown in the Table F below. Polymer is coagulated bydiluting the dispersion to about 10 wt % solids and adding aqueousammonium carbonate solution followed by vigorous agitation until thepolymer fully separates from the water The polymer is dried in a vacuumoven at 110° C. for 12 hours. The PTFE exhibits the molecular weight andmelt creep viscosity characteristics of the PTFE described in Example 2.

TABLE E PT Batch Temp. Time Dv(50) Experiment ° C. min. nm E-1 22 110.1188 E-2 30 109.2 176 E-3 40 152.4 197The batch time falls sharply from passivation of the stabilizingsurfactant at 40° C. to passivation at lower temperatures.

Example 7

The Example compares polymerization performance using passivated andunpassivated stabilizing surfactant

To a 12 liter, horizontally disposed, jacketed, stainless steel reactorwith a two blade agitator is added 5200 gm of deionized, deaerated waterand 250 gm of liquid wax. To the reactor is added an additional 500 gmof deionized, deaerated water which contains 0.075 gm of Pluronic® 31R1and 0.2 gm of sodium sulfite. The reactor is sealed and placed undervacuum. The reactor pressure is raised to 30 psig (310 kPa) withnitrogen and brought to vacuum three times. Reactor agitator is set at65 RPM. The reactor is heated to 90° C. and 100 ml of initiatorcontaining 0.5 gm APS per liter of deionized, deaerated water is addedto the reactor, providing an APS concentration of 8.6 ppm in theprecharge composition. The concentration of the surfactant in theaqueous medium is 12.9 ppm and of the salt is 34.5 ppm.

690 gm of TFE is added to the reactor to bring the reactor pressure to400 psig (2.86 MPa). At time zero, 150 ml of initiator solutioncontaining 0.5 gm APS per liter of deionized deaerated water is chargedto the reactor at 80 ml/min and then the pump rate is reduced to 1.0ml/min for the duration of the polymerization. Kickoff is measured asthe time (since time zero) necessary to drop 10 psi (69 kPa) from themaximum pressure observed during injection of the charge initiatorsolution. Kickoff occurs in 2 minutes and the reactor pressure isbrought back to 400 psig (2.86 MPa) with makeup TFE and maintained atthat pressure for the duration of the polymerization by continuousaddition of makeup TFE. After 300 gm of makeup TFE has been added to thereactor, a pump solution containing 8.0 gm of sodium dodecyl sulfate perliter of water is added to the reactor at a rate of 2.0 ml/min until atotal of 300 gm of solution has been added. The time delay betweenkickoff and commencement of the SDS addition is 9.3 min, theconcentration of PTFE in the aqueous medium at the end of this timedelay is 4.79 wt %, and the surfactant metering rate is 0.08 g/l-hr.After 197 minutes from time zero, 2200 gm of makeup TFE has been addedto the reactor, the agitator is stopped, the reactor is vented toatmospheric pressure and the dispersion is discharged. Batch time is 195min (calculation: 197 min-2 min). PTFE dispersion thus made has 28%solids and a raw dispersion particle size of 213 nm. A polymer sample isobtained by diluting a quantity of dispersion to approximately 10 wt %solids, adding an aqueous solution of ammonium carbonate and vigorouslyagitating to separate the polymer from the aqueous phase. Polymer iswashed with deionized water and dried in a vacuum oven at 110° C. forapproximately 12 hours before being further analyzed. The PTFE exhibitsthe molecular weight and melt creep viscosity characteristics of thePTFE as described in Example 2.

The above experiment is repeated except that after 300 gm of makeup TFEis added to the reactor, a pump solution containing 14.4 gm ofpassivated sodium dodecyl sulfate per liter of water is added to thereactor at a rate of 1.67 ml/min until the end of the run at which time2200 gm of makeup TFE has been added to the reactor. The delay incommencing the addition of the passivated SDS to the aqueous medium is9.7 min, the PTFE concentration at the end of the delay is 4.79 wt %,and the metering rate of the surfactant into the aqueous medium is 0.12g/l-hr. Total quantity of passivated sodium dodecyl sulfate solutionadded is 115 ml. The batch time of 79 minutes is significantly less thanthe unpassivated experiment in the preceding paragraph. The dispersionmeasures 26.5% solids and has a raw dispersion particle size of 175 nm.The PTFE exhibits the molecular weight and melt creep viscositycharacteristics of the PTFE as described in Example 2.

The passivation of the SDS is carried out by the following procedure:Into a 1 liter, jacketed round bottom flask is added 681.74 gm ofdeionized, deaerated water, 10.5 gm of sodium dodecyl sulfate (ACSReagent, >99.0%) and 0.315 gm of iron(⁺²) sulfate heptahydrate. Thecontents are agitated until all solids are dissolved. The solution pH isadjusted to 2.0-2.5 with 12-18 drops of concentrated sulfuric acid.While holding the mixture at 22° C. by circulating thermally regulatedwater through the flask jacket, 37.34 gm of 30 wt % hydrogen peroxide isadded to the mixture. The mixture is agitated for 1 hour before beingdischarged for use as the solution of passivated stabilizing surfactantin polymerization.

Example 8

This Example discloses the polymerization to make PTFE using anethoxylated anionic surfactant as the stabilizing surfactant.

To a 12 liter, horizontally disposed, jacketed, stainless steel reactorwith a two blade agitator is added 5200 gm of deionized, deaerated waterand 250 gm of liquid wax. To the reactor is added an additional 500 gmof deionized, deaerated water which contains 0.085 gm of Pluronic® 31R1,0.02 gm of Triton® X-100 and 0.4 gm of Na₂SO₃. The reactor is sealed andplaced under vacuum. The reactor pressure is raised to 30 psig (310 kPa)with nitrogen and brought to vacuum three times. Reactor agitator is setat 65 RPM and the reactor is heated to 90° C. 80 ml of initiatorsolution containing 0.5 gm of ammonium persulfate (APS) per liter ofdeionized, deaerated water is added to the reactor, providing an APSconcentration in the aqueous precharge of 6.9 ppm. The concentrations ofthe surfactants in the aqueous medium are 14.7 ppm and 3.5 ppm,respectively, and the salt concentration is 69.2 ppm. TFE is charged tothe reactor to bring the reactor pressure to 400 psig (2.86 MPa). Attime zero, 150 ml of an initiator solution in deionized, deaerated watercontaining 0.33 gm APS and 23.33 gm of 70 wt % active disuccinic acidperoxide (DSP) per liter of water is charged to the reactor at 80ml/min. Kickoff time is measured as the time (since time zero) necessaryto drop 10 psi (69 kPa) from the maximum pressure observed duringinjection of the initiator solution at time zero. Kickoff occurs in 6.8minutes. The reactor pressure is brought back to 400 psig (2.86 MPa)with makeup TFE and maintained at that pressure by adjusting makeup TFEflow for the duration of the polymerization. After 100 gm of makeup TFEhas been fed, a passivated stabilizing solution containing Avanel® S70is pumped at a rate of 4 ml/min until the end of the run. The time delayin commencing the addition of stabilizing surfactant to the aqueousmedium is 7.9 min, the wt % delay corresponds to a PTFE concentration inthe aqueous medium of 1.66 wt %, and the metering rate of the surfactantinto the aqueous medium is 0.288 g/l-hr. After 2200 gm of TFE has beenadded to the reactor since Time Zero, the agitator is stopped, thereactor is vented to atmospheric pressure and the dispersion isdischarged. The resultant aqueous dispersion has 24.7% solids having anaverage particle size by volume, Dv(50), of 178 nm. Polymer iscoagulated by diluting the dispersion to about 10 wt % solids and addingaqueous ammonium carbonate solution followed by vigorous agitation untilthe polymer fully separates from the water. The PTFE is dried in avacuum oven at 110° C. for 12 hours, and it is determined to exhibit themolecular weight and melt creep viscosity characteristics of the PTFE ofExample 2.

The procedure for passivating the Avanel® surfactant is as follows: To a1 liter glass bottle is added 30 gm of Avanel® S70 solution (10.5 gmactive surfactant), 662.24 gm of deionized, deaerated water and 0.315 gmof iron(+2) sulfate heptahydrate. The mixture is stirred until allsolids are dissolved. pH of this mixture is adjusted to 2.0-2.5 with 12to 16 drops of concentrated sulfuric acid. While agitating and holdingat 22-23° C., 37.34 gm of 30 wt % hydrogen peroxide is slowly added tothe mixture over a period of 1 to 2 minutes. After addition of thehydrogen peroxide stirring is continued for 1 hour before the resultingpassivated surfactant solution is used in the above polymerization.

Example 9

This Example discloses the polymerization to make PTFE using a varietyof anionic hydrocarbon stabilizing surfactants.

To a 12 liter, horizontally disposed, jacketed, stainless steel reactorwith a two blade agitator is added 5200 gm of deionized, deaerated waterand 250 gm of liquid wax. To the reactor is added an additional 500 gmof deionized, deaerated water which contains 0.085 gm (14.7 ppm) ofPluronic® 31R1, and 0.4 gm (69 ppm) of sodium sulfite. The reactor issealed and placed under vacuum. The reactor pressure is raised to 30psig (310 kPa) with nitrogen and brought to vacuum 3 times. The agitatorspeed is set to 65 RPM and the reactor is heated to 90° C. 80 ml of asolution containing 0.5 gm of ammonium persulfate (APS) initiator perliter of water is added to the reactor, providing an APS concentrationin the water added so far to the reactor of 6.9 ppm. This is the stageof the reaction wherein oleophilic nucleation sites are formed prior tokickoff of the polymerization reaction. The ppm of ingredients added tothe aqueous medium stated above are based on the total amount of waterpresent in the reactor up until this time.

TFE is next charged to the reactor to bring the reactor pressure to 400psig (2.86 MPa). 150 ml of an initiator solution composed of 11.67 gm of(70% active) disuccinic acid peroxide, 0.17 gm of ammonium persulfateand 488.3 gm of deionized water is charged to the reactor at 80 ml/min.Kickoff of the polymerization reaction is considered to have occurredafter a drop of 10 psi (69 kPa) from the maximum pressure observedduring injection of the initiator solution. Reactor pressure is broughtback to 400 psig (2.86 MPa) with makeup TFE and maintained at thatpressure for the duration of the polymerization by continuous additionof makeup TFE. After 100 gm of TFE has been fed since kickoff,corresponding to a PTFE concentration of 2.49 wt % in the aqueousmedium, an aqueous solution of surfactant and metal ions identified inTable F is pumped to the reactor at a rate of 4 ml/min (surfactantmetering rate=0.288 g/l-hr) until the end of the run, i.e. until theaddition of makeup TFE to the reactor is stopped. After the prescribedamount of makeup TFE has been added to the reactor, the TFE feed andagitator is stopped, this establishing the completion of thepolymerization reaction. After venting of the reactor (removal ofunreacted TFE), the polymer dispersion is discharged. Upon cooling,liquid wax is separated from the dispersion and the dispersion isfiltered to remove undispersed solids. The reactor is opened and alladhered polymer removed from the reactor. Reactor cleanout is combinedwith the filtered solids and dried in a vacuum oven.

Coagulum (total undispersed solids) is obtained by further removingliquid wax from the dry filtered solids plus adhered polymer bycentrifuging and blotting the polymer to remove wax. The polymerdispersion is coagulated by diluting the dispersion water to about 10 wt% solids and adding aqueous ammonium carbonate solution followed byvigorous agitation until the polymer fully separates from the water. Theresultant polymer is dried in a vacuum oven at 110° C. for 12 hours.Melting point and heat of fusion of this polymer is determined byDifferential Scanning calorimeter (DSC). The polymer is PTFE having amolecular weight (Mn) of at least 1,000,000.

The results of these experiments are reported in Table F below.

TABLE F Surfactant Solution Pumped Surf. ppm Wt % Salt ppm cation cationExp. Conc. on on on # gm/L Surf. water SALT water* Surf. F-1 0.432 SDS627 FeSO4—7H2O 3.8 0.6032 F-2 0.388 SDS 659 CuSO4—5H2O 4.5 0.6751 F-30.432 K8300 1098 FeSO4—7H2O 6.6 0.6031 F-4 0.388 S-74 1366 CuSO4—5H2O9.4 0.6863 F-5 0.388 S-70 994 CuSO4—5H2O 6.8 0.6863 Batch Dispersion STYExp. Time % Dv(50) Coag. gm/ # min Solids nm % (L-hr) F-1 72.9 27.48 1831.66 162.8 F-2 76.4 26.99 161 0.17 150.4 F-3 125.9 26.67 199 2.52 92.9F-4 162.8 26.27 154 0.23 72.9 F-5 118.3 26.33 153 3.26 94.8 *cation isthe metal ionThe “Surf. ppm on water” is the total weight of stabilizing surfactantadded to the total weight of water added to the polymerization reactoruntil completion of the polymerization reaction. The “ppm cation onwater” is the weight ppm of the metal ion in the total amount of wateradded to the reactor until completion of the polymerization reaction.“Batch time” is measured as the time from polymerization kickoff to thecompletion of the polymerization reaction. The “Dispersion % Solids” isthe wt % of the polymer particles dispersed in the aqueous medium ascompared to the total weight of the dispersed polymer particles+thetotal weight of water present at completion of the polymerizationreaction. STY (space-time-yield of the polymerization reaction is ameasure of productivity of the polymerization reaction). In STY, spaceis the volume of the reactor, time is the time from kickoff of thepolymerization reaction until its completion, and yield is the weight ofdispersed polymer formed. STY is expressed herein as gm (of dispersedpolymer)/l-hr.

All of the polymerizations reported in Table F produce small particlesat the high % solids obtained, together with low % coagulum and goodSTY. The melting temperatures of the PTFEs produced all exceed 335° C.and the reduction in heats of fusion from the first heat to the secondheat melting all exceed 29 J/gm.

The PTFEs obtained in the foregoing Examples all exhibit an MFR of 0(ASTM D 1238 at 372° C. and 5 kg. wt.) as another indication of thenon-melt flowability of these PTFEs because of their extremely highmolecular weight.

Example 10

This Example discloses Aspects A, B, and C of an embodiment of thepresent invention directed to the preparation of high solids contentaqueous dispersion of PTFE particles, i.e. solids contents of 45 wt %and greater than 45 wt %, preferably 50 wt % and greater than 50 wt %,and more preferably 55 wt % and greater than 55 wt %, and up to 60 wt %or 65 wt % by polymerization, wherein the stabilizing surfactant ishydrocarbon surfactant. The disclosure hereinafter in this Exampleapplies to each of these high solids contents. The “solids” in “solidscontents” are the dispersed PTFE particles.

The practice of Aspect A of this embodiment involves the use of a muchgreater amount of hydrocarbon-containing surfactant, preferablyhydrocarbon surfactant, metered to the aqueous medium for stabilizingthe PTFE dispersion during the polymerization reaction. For example, thecontrol experiment in Table G below uses 724 ppm total stabilizingsurfactant concentration based on the total weight of dispersed PTFEparticles to obtain a dispersion solids content in the aqueous medium of33.9% (34 wt %). Aspect A uses more than 1.5× this amount, preferably atleast 2× this amount, more preferably at least 3× this amount and mostpreferably at least 4× this amount, notwithstanding the warning in U.S.Pat. No. 3,000,892 to Duddington that “these dispersing agents[hydrocarbon dispersing agents] normally inhibit the polymerization oftetrafluoroethylene” (col. 1, I. 65-66). Example II in '892 uses 2645ppm of sodium lauryl sulfate (SDS) based on the total weight of PTFEpresent as dispersed particles to polymerize TFE to a PTFE dispersion inwhich the solids content reaches only 8.4 wt %.

Surprisingly, the use of a large amount of hydrocarbon-containingstabilizing surfactant in Aspect A is without appreciable loss inproductivity of the reactor, which can be determined by space-time-yield(STY) of the polymerization reaction. Preferably the STY to produce thesolids content of at least 45 wt % is at least 90% of the STY of thesame polymerization process, except that the total amount ofhydrocarbon-containing surfactant is smaller to provide the 34 wt %solids content. The use of a smaller amount of such surfactant to obtain34 wt % (33-35 wt %) arises from the desire to minimize the amount oftotal surfactant so as to reduce telogenic effect on the polymerizationreaction. More preferably, there is no decrease in such STY of thepolymerization reaction. More preferred, and surprisingly, the STY isincreased as compared to the aforesaid polymerization to obtain a solidscontent of 34 wt %, and this increase is preferably at least 5% morepreferably, at least 10%.

The limitation on solids content of 8.4 wt % in Example II of '892 isthe PTFE particle size of 0.23 micrometers obtained at this low solidscontent. This is a large particle size for so early in the particlegrowth stage represented by the solids content of only 8.4 wt %. Theincrease in particle size from 0.23 micrometers if the polymerizationwere driven to a higher solids content can be seen from information inthe present application. Specifically, Experiment A-1 in Example 1 ofthe present application reports that the particle size of 198 nm at asolids content of 11.75 wt % grows to a 311 nm particle size if thepolymerization were continued to 34 wt % solids content. Such a largeparticle size is undesirable because it reduces the stability of thedispersion of the particles, promoting the formation of coagulum. Incontrast, the PTFE particle size of high solids content dispersionsreported in Table G reveal much smaller PTFE particle sizes for the muchhigher solids contents of 45 wt % and higher.

It has been discovered that metering of the hydrocarbon-containingsurfactant to the aqueous polymerization medium during polymerization tototal a much greater amount of the surfactant enables the polymerizationto be carried out to produce a stable dispersion having a substantiallygreater solids content, without any appreciable sacrifice inproductivity as indicated by STY of the polymerization reaction.Accompanying this discovery is the additional surprise that theincreased amount of hydrocarbon-containing stabilizing surfactant usedin this embodiment of the present invention, while expected to inhibitthe polymerization of TFE to make PTFE, does not inhibit suchpolymerization. The resultant PTFE forming the dispersed particles inthe aqueous polymerization medium is of high molecular weight, i.e.having a molecular weight of at least 1,000,000, as indicated bynon-melt flowability and DSC melting temperature (first heat) of atleast 332° C.

Thus, Aspect A of the embodiment of this Example can be described as aprocess for polymerizing fluoromonomer to form a dispersion offluoroplastic particles in an aqueous medium in a polymerizationreactor, comprising steps (a), (b), (c) and (d) recited above, andfurther wherein the fluoroplastic is polytetrafluoroethylene and thepolymerizing is carried out to wherein the dispersion ofpolytetrafluoroethylene particles constitute at least 45 wt % of theaqueous medium. The total amount of hydrocarbon-containing surfactantmetered into the aqueous medium is preferably effective to provide thisdispersion of at least 45 wt % of the aqueous medium.

As with lower solids contents dispersions of fluoroplastic particlesmade by polymerization in accordance with the present invention, theaqueous medium is essentially free of hydrocarbon-containing surfactantbefore the kicking off of the polymerization of the fluoromonomer,notwithstanding that hydrocarbon-containing nucleant surfactant may havebeen added to the aqueous medium to be oxidatively degraded tooleophilic nucleation sites prior to polymerization kickoff. Prior topolymerization kickoff, the aqueous medium is preferably alsoessentially free of halogen-containing surfactant and preferably no suchsurfactant is added to the polymerization medium during or after thekicking off of the polymerization reaction. The aqueous mediumcontaining the dispersion of PTFE particles upon completion of thepolymerization, i.e. as polymerized, is also preferably essentially freeof halogen-containing surfactant, such as fluorosurfactant. Morepreferably, the aqueous medium is free of halogen-containing surfactant,meaning that no such surfactant has been added to the aqueous medium.The hydrocarbon-containing surfactant is essentially the only surfactantstabilizing the as-polymerized high solids content PTFE particle aqueousdispersion.

The disclosures under SUMMARY OF THE INVENTION and DETAILED DESCRIPTIONOF THE INVENTION earlier in this patent application apply to theembodiment of this Example, which includes all of its Aspects. Thus, thedescription of the PTFE earlier in the present application in thesection under Fluoromonomer/Fluoroplastic is applicable to the PTFE ofthis embodiment. The disclosure in the section under The PolymerizationProcess earlier herein is also applicable to this embodiment, includinge.g. the delay after polymerization kickoff before the addition of thehydrocarbon stabilization surfactant is commenced, the metering rate ofthis addition, the identity of the hydrocarbon-containing surfactant,the polymerization initiators that are used, the coagulum amounts, withthe following exceptions: the wt % PTFE solids contents are higher thanthose mentioned under The Polymerization Process and the concentrationstep of adding surfactant to the aqueous dispersion after polymerizationis completed to enable the dispersion to be concentrated to highersolids contents is unnecessary. High solids contents are obtaineddirectly by polymerization without the need for a concentration stepsuch as disclosed in U.S. Pat. No. 3,037,953 (Marks and Whipple). Thedispersion of PTFE particles in the aqueous medium is also preferablyfree of anionic polyelectrolyte disclosed in US2007/0282044A as being analternative to the anionic surfactant added to the aqueous dispersionafter polymerization to enable the dispersion to be concentratedaccording to '953. With high solids contents represented by solidscontent of 45 wt % and greater than 45 wt %, any coagulum formation ispreferably very small, e.g. 2 wt % or less than 2 wt % and morepreferably 1 wt % or less than 1 wt %. This is a surprisingaccomplishment, in that the higher the solids content of the aqueousdispersion, the greater is the tendency for coagulum wt % to alsoincrease. The high solids PTFE dispersions of the embodiment of thisExample can be obtained with very small coagulum wt % as shown in TableG.

The preferences disclosed in each of these sections under ThePolymerization Process are also applicable to the embodiment of thisExample. Also applicable to this embodiment is passivation of thehydrocarbon-containing surfactant disclosed under Passivation of theHydrocarbon-Containing Surfactant, including the preferences disclosedthereunder.

Also applicable to the embodiment of this Example is the formation ofpolymerization sites in the aqueous medium prior to polymerizationkickoff as disclosed under Polymerization Sites, including thepreferences disclosed thereunder. The preference for the formation ofpolymerization sites that are oleophilic nucleation sites includes theaddition of a small amount of hydrocarbon-containing surfactant(nucleant surfactant) to the aqueous medium, preferably no greater than50 ppm of the nucleant surfactant) to be subjected to oxidativedegradation, leaving the aqueous medium essentially free of nucleantsurfactant at the time of kick off of the polymerization reaction.

In the practice of Aspect A, preferably, the total amount ofhydrocarbon-containing stabilizing surfactant added to the aqueousmedium is 3000 ppm and greater than 3000 ppm, more preferably 3500 ppmand greater than 3500 ppm, and most preferably 4000 ppm and greater than4000 ppm, based on the total weight of PTFE present as dispersedparticles, whether solids content is at least 45 wt %, at least 50 wt %or at least 55 wt %. As the solids content is increased above 45 wt %,so does the preferred total amount of hydrocarbon surfactant. Thegreater amount of stabilizing surfactant as compared to that which isneeded to produce a solids content of 34 wt % PTFE involves twodifferences from the metering preferred for obtaining a dispersion ofPTFE particles providing a solids content of 34 wt %: increase in themetering amount and increase in the duration of metering, preferablywithout sacrifice in STY. Instead an increase in STY is obtained, e.g.an increase by at least 10% (calculation: [100−(STY for 34 wt % solidscontent/STY for 60 wt %)]×100). The preferred metering rate of thestabilizing surfactant into the aqueous medium is from 0.7 g/l-hr to 1.4g/l-hr as compared to the much smaller metering rates disclosed inearlier Examples for making PTFE in the present application. The maximumtotal amount of hydrocarbon-containing stabilizing surfactant isestablished by the high solids content desired along with the desiredSTY and minimized coagulum wt %. The maximum total amount should notpenalize STY as described above and should produce a coagulum wt % 2 wt% or less than 2 wt %, more preferably, 1 wt % or less than 1 wt %.Generally, the total amount of hydrocarbon-containing surfactant addedto the aqueous medium will be no greater than 5500 ppm, based on theweight of the dispersed particles of PTFE

Aspect B of the embodiment of this Example can be described as follows:In a polymerization reactor, a dispersion of PTFE particles in anaqueous medium having a solids content of the particles in the aqueousmedium of 45 wt % or greater than 45 wt %, wherein the dispersion ismaintained stable within the aqueous medium by hydrocarbon-containingsurfactant. By “maintained stable” is meant that without the presence ofthe hydrocarbon-containing stabilizing surfactant, the dispersion isunstable, i.e. the particles of PTFE coagulate within the reactor duringthe polymerization reaction. Coagulation during the polymerizationreaction is exponential in the sense that once a small amount ofcoagulum is formed, e.g. 2 to 4 wt %, the formation of coagulum tends toincrease thereafter at a more rapid rate to higher coagulum wt % s. Itis this exponential increase in coagulum wt % that has generally limitedpolymerizations to less than 40 wt % solids contents for PTFE aqueousdispersions. If any other surfactant is present in the aqueousdispersion, such other surfactant does not stabilize the dispersion ofPTFE particles. The dispersion is stable during the stirringaccompanying the polymerization reaction and after the stirring hasstopped upon completion of the reaction, resulting in the low coagulumwt % s described above in this Example and the ability to remove thedispersion from the reactor and store it without detriment to thedispersion.

Aspect C of the embodiment of this Example can be described as follows:A dispersion of PTFE particles in an aqueous medium having a solidscontent of the particles in the aqueous medium of at least 45 wt %,wherein the dispersion is maintained stable as described above withinthe aqueous medium by hydrocarbon-containing surfactant.

In Aspects A, B, and C, the preferred hydrocarbon-containing stabilizingsurfactant is anionic hydrocarbon surfactant, e.g. any of thosedisclosed above. In Aspects A, B and C, the preferred amounts ofsurfactant, preferably ionic surfactant added to or present in theaqueous medium is 3000 ppm or greater than 3000 ppm, more preferably3500 ppm or greater than 3500 ppm, and most preferably 4000 ppm orgreater than 4000 ppm, based on the total weight of PTFE present asdispersed particles, whether solids content is at least 45 wt %, atleast 50 wt % or at least 55 wt %. These amounts also apply to thepreferred anionic surfactant R-L-M described, especiallyCH₃—(CH₂)_(n)-L-M wherein n, L, and M are described above, and mostespecially to sodium dodecyl sulfate (SDS). In Aspects B and C, theaqueous medium is essentially free of hydrocarbon-containing surfactantother than the hydrocarbon-containing surfactant that stabilizes thehigh solids content dispersion of PTFE particles. In the practice ofAspects A and B, any hydrocarbon-containing surfactant added to theaqueous medium before the kicking off of the polymerization of thefluoromonomer is oxidatively degraded to oleophilic nucleation sitesprior to polymerization kickoff. In Aspect B, the aqueous medium uponcompletion of the polymerization is also preferably essentially free ofhalogen-containing surfactant, most preferably free ofhalogen-containing surfactant, such as fluorosurfactant in each case.This also applies to the aqueous dispersion of PTFE particles of AspectC. The aqueous dispersion of Aspect C is also preferably as-polymerized.In Aspects A and B, the hydrocarbon-containing surfactant is essentiallythe only surfactant maintaining the stability of the high solids contentPTFE particle dispersion in the aqueous medium, preferably aspolymerized.

Illustrative of the practice of the embodiment of this Example is thefollowing experiment.

To a 12 liter, horizontally disposed, jacketed, stainless steel reactorwith a two blade agitator is added 3100 gm of deionized, deaerated waterand 250 gm of liquid wax. To the reactor is added an additional 500 gmof deionized, deaerated water which contains 0.120 gm of Pluronic® 31R1and 0.07 gm of Tergitol® TMN-6. The reactor is sealed and placed undervacuum. The reactor pressure is raised to 30 psig (310 kPa) withnitrogen and vented to atmospheric pressure. The reactor is pressuredwith nitrogen and vented 2 more times. The agitator speed is set to 65RPM and the reactor is heated to 90° C. 160 ml of initiator solutioncontaining 2.0 gm of ammonium persulfate (APS) per liter of water isadded to the reactor. 948 gm of TFE is charged to the reactor to bringthe reactor pressure to 400 psig (2.86 MPa). At time zero, 150 ml of aninitiator solution composed of 14.58 gm of disuccinic acid peroxide,0.18 gm of ammonium persulfate and 485.2 gm of deionized water isprecharged to the reactor at 80 ml/min. After 2.6 minutes from the startof initiator injection the reactor pressure drops 10 psi (69 kPa) fromthe maximum pressure observed during injection of the initiatorsolution. Reactor pressure is brought back to 400 psig (2.86 MPa) withTFE and maintained at that pressure for the duration of thepolymerization. After 100 gm of TFE has been fed since kickoff,corresponding to a 1.66 wt % concentration of PTFE in the aqueousmedium, surfactant solution containing 7.0 gm of SDS as the hydrocarbonstabilizing surfactant and 0.043 gm of iron sulfate heptahydrate per 100gm of water is pumped to the reactor at a rate of 3 ml/min (1.05 gm/l-hrof SDS) until the end of the run. After 153 minutes since kickoff, 6500gm of TFE and 444 ml of surfactant solution has been added to thereactor. The agitator is stopped, the reactor is vented to atmosphericpressure and the dispersion is discharged. Upon cooling, liquid wax isseparated from the dispersion and the dispersion is filtered to removeundispersed solids. The reactor is opened and all adhered polymerremoved from the reactor. Reactor cleanout is combined with the filteredsolids and dried in a vacuum oven. To get a measure of coagulum (totalundispersed solids) liquid wax adhering to this polymer is furtherremoved by centrifuging the polymer. Total coagulum is thus determinedto be 29.1 gm. 6461 gm of dispersed PTFE particles, providing a solidscontent in the aqueous medium of 59.1% and an average particle size byvolume, Dv(50), of 233 nm. The total amount of SDS added to the aqueousmedium is 4810 ppm based on the weight of the PTFE particles of thedispersion. STY is 208.8 g/l-hr. The dispersion of PTFE particles iscoagulated by diluting the dispersion to about 10 wt % solids and addingaqueous ammonium carbonate solution followed by vigorous agitation untilthe polymer fully separates from the water. The PTFE is dried in avacuum oven at 110° C. for 12 hours. Melting point of the PTFE asmeasured by DSC on first heat is 337.8° C. This experiment is G-16 inTable G below.

A large number of polymerizations are carried out essentially followingthe above polymerization procedure, but varying the total amount ofhydrocarbon surfactant to the aqueous medium, with the results obtainedbeing reported in Table G below.

TABLE G Total Total Dispersed STY Surf. % PTFE Coagulum gm/ Exp ppmSolids Dv(50) gm wt % l-hr Control 724 33.9 224 3267 2.3 148 G-1 132147.6 245 4543 5.8 189 G-2 1777 49.0 248 5022 5.6 201 G-3 1905 50.4 2255512 6.3 148 G-4 2406 53.0 232 5610 4.4 156 G-5 2669 53.1 237 5621 3.6161 G-6 2943 52.1 230 5607 3.3 166 G-7 3012 53.7 233 6025 2.0 176 G-83081 53.3 234 5842 1.8 136 G-9 3126 52.4 231 5806 1.1 156 G-10 3881 54.3223 6262 0.7 174 G-11 4038 54.6 247 6129 0.8 128 G-12 4149 59.3 240 68691.1 182 G-13 4273 57.7 238 6670 0.7 175 G-14 4475 55.1 236 6369 0.6 189G-15 4479 56.9 232 6357 0.7 208 G-16 4810 59.1 233 6461 0.4 209 G-174653 60.4 242 6770 0.6 208In Table G, the surfactant is SDS, the control is polymerization using724 ppm of SDS to obtain a solids content of 33.9 wt %. Ppm ofSurfactant is based on the total dispersed PTFE produced.

The results in Table G show that as the total amount of SDS (Total Surfppm) increases above 724 ppm, the coagulum wt % increases sharply up toabout 2000 ppm SDS, followed by a decline through the 2000-3000 ppm SDSrange, wherein the coagulum wt % is higher than desired for high %solids dispersions. For example, the coagulum wt % for G-5 correspondsto 211 gm of coagulum, as compared to 77 gm of coagulum for the Controlexperiment. Within the 3000-4000 ppm SDS range, the wt % coagulumundergoes a transition, essentially from coagulum wt % of 2.0 wt % toless than 1.0 wt %. At 3012 ppm of total SDS added to the aqueous medium(G-7), the % coagulum is 2.0 wt %, while at 3881 ppm of total SDS addedto the aqueous medium, the coagulum wt % is only 0.7 wt %. At total SDSamounts of at least 4000 ppm based on the total dispersed PTFE, thecoagulum wt % s are consistently low, 6 out of 7 being less than 1.0coagulum wt %. Experiment G-16 shows that a 59% solids contentdispersion can have a coagulum wt % of considerably less than 1. Thesame is true for the 60.4 wt % solids of Experiment G-17. ExperimentsG-1 through G-6, producing undesirable coagulum wt % s at the highsolids indicated, can be improved upon in this regard, by for examplerepeating the polymerization such as G-10, but stopping (completing) thepolymerization at a lower solids content, such as 45 wt % or 50 wt %.The coagulum wt % of 0.7 for G-10 will be no higher when thepolymerization is stopped upon reaching such lower solids content.

All of the PTFE polymers produced in these runs are high molecularweight, non melt flowable polymers, having a DSC first heat meltingtemperature of at least 336° C.

Example 11

This Example provides the preparation of TFE/VF₂ fluoroplastic

To a 12 liter, horizontally disposed, jacketed, stainless steel reactorwith a two blade agitator is added 6000 gm of deionized, deaeratedwater. To the reactor is added an additional 500 gm of deionized,deaerated water which contains 0.2 gm of Pluronic® 31R1. The reactor issealed and placed under vacuum. The reactor pressure is raised to 30psig (310 kPa) with nitrogen and evacuated three times. Agitation isbegun and the agitator speed is set to 65 RPM. 0.5 gm of ethane is addedto the reactor and the reactor is heated to 80° C. 30 ml of initiatorsolution containing 6.2 gm ammonium persulfate per liter of water isadded to the reactor before precharging with monomers. A monomer mixtureof 61 wt % TFE and 39 wt % VF₂ is charged to the reactor to bring thereactor to an operating pressure of 350 psig (2.51 MPa). When atoperating pressure, 75 ml of initiator solution is charged to thereactor at 25 ml/min and then the pump rate is reset to 0.5 ml/min forthe duration of the polymerization run. Kickoff occurs after 7 minutesfrom the start of initiator injection when the reactor pressure drops 10psi (69 kPa) from the maximum pressure observed during injection of theinitiator solution. Reactor pressure is controlled at 350 psig (2.51MPa) with addition of a monomer mixture containing 55 wt % TFE and 45 wt% VF₂. After 500 gm of monomer has been fed since kickoff, correspondingto 7.02 wt % of TFE/VF₂ copolymer in the aqueous medium, a surfactantsolution is pumped to the reactor at a rate of 0.2 ml/min until the endof the run. The surfactant solution is composed of 14.39 gm of sodiumdodecyl sulfate per liter of solution which has been adjusted to a pH of2.27 by the addition of sulfuric acid. The metering rate of the SDS is0.0144 g/l-hr. After 99 minutes since kickoff, 1500 gm of monomermixture and 13 ml of surfactant solution has been added to the reactor.The agitator is stopped, the reactor is vented to atmospheric pressureand the fluoropolymer dispersion is discharged. 7.43 kg of dispersion isproduced with 16.1 wt % solids content and 212 nm raw dispersionparticle size. Coagulum obtained from cleaning the reactor is dried in avacuum oven and measures 46.6 gm. Polymer is isolated by freezing adispersion sample followed by thawing, filtration, washing and drying.The polymer has a melting point as measured by Differential Scanningcalorimeter of 175.4° C. and a heat of fusion of 34 Joules/gm, bothindicating that the polymer is fluoroplastic, not a fluoroelastomer Thecopolymer has a very high molecular weight as indicated by difficulty incompression molding the copolymer into a film, i.e. the copolymer has ahigh melt viscosity characteristic of perfluoroplastics. Thecompression-molded film is dimensionally stable (not deformable like afluoroelastomer) and is flexible.

What is claimed is:
 1. Process for polymerizing fluoromonomer to form adispersion of fluoropolymer particles in an aqueous medium in apolymerization reactor, comprising (a) providing an aqueous medium insaid reactor, (b) adding said fluoromonomer to said reactor, (c) addingpolymerization initiator to said aqueous medium, thereby kicking offsaid polymerizing of said fluoromonomer, said kicking off beingindicated by a pressure drop in the reactor of at least 10 psi, and (d)metering hydrocarbon surfactant into said aqueous medium after saidkicking off of said polymerization, wherein said metering of saidhydrocarbon surfactant commences when the concentration of saidfluoropolymer in said aqueous medium is at least 0.6 wt %, and whereinsaid metering of hydrocarbon surfactant into said aqueous medium is at ametering rate of at least 0.005 g/l-hr and provides an amount ofhydrocarbon surfactant in the aqueous medium sufficient to stabilize thedispersion of fluoropolymer particles formed during polymerization, andwherein said aqueous medium comprises no more than 50 ppm of surfactantbased on the weight of surfactant divided by the weight of water presentin the reactor before said kicking off of said polymerizing of saidfluoromonomer and no halogen-containing surfactant is added to saidaqueous medium during or after said kicking off of said polymerization.2. The process of claim 1 wherein said metering is at a rate reducingthe telogenic activity of said hydrocarbon surfactant while maintainingsurface activity to stabilize said dispersion of fluoropolymer particlesin said medium during said polymerizing.
 3. The process of claim 1wherein said hydrocarbon surfactant is anionic.
 4. The process of claim1 wherein said metering includes the addition of said hydrocarbonsurfactant to said aqueous medium at least every 20 min.
 5. The processof claim 1 includes the addition of said hydrocarbon surfactant to saidaqueous medium at a rate of 0.005 to 1.4 g/l-hr.
 6. The process of claim1 wherein said fluoropolymer is polytetrafluoroethylene and saidpolymerizing is carried out to wherein said dispersion ofpolytetrafluoroethylene particles constitute 45 wt % or greater than 45wt % of said aqueous medium.
 7. The process of claim 6 wherein the totalamount of hydrocarbon surfactant metered into said aqueous medium iseffective to provide said dispersion of 45 wt % or greater than 45 wt %of said aqueous medium.
 8. The process of claim 7 wherein said totalamount of said hydrocarbon surfactant is 3000 ppm or greater than 3000ppm, based on the weight of said polytetrafluoroethylene particles. 9.The process of claim 1 further comprising passivating said hydrocarbonsurfactant.
 10. The process of claim 9 wherein said passivating reducesthe telogenicity of said hydrocarbon surfactant so as to reduce the timeof said polymerizing.
 11. The process of claim 9 wherein saidpassivating is carried out by oxidizing said hydrocarbon surfactant. 12.The process of claim 11, wherein said passivating is carried out in thepresence of passivation adjuvant.
 13. The process of claim 1 furthercomprising providing polymerization sites dispersed in said aqueousmedium prior to said kickoff of said polymerizing of said fluoromonomer.14. The process of claim 13 wherein said polymerization sites containfluorine-containing polymer.
 15. The process of claim 13 wherein saiddispersion of polymerization sites are hydrocarbon-containing.
 16. Theprocess of claim 15, wherein said dispersion of hydrocarbon-containingpolymerization sites is made by adding no more than 50 ppm of awater-soluble hydrocarbon-containing compound containing hydrophobicmoiety and hydrophilic moiety to said aqueous medium and exposing saidhydrocarbon-containing compound to degradation of said hydrophilicmoiety, thereby enabling said hydrophobic moiety to form said dispersionof polymerization sites.
 17. The process of claim 16 further comprisingadding water-soluble inorganic salt to said aqueous medium prior to saidexposing of said hydrocarbon-containing compound to said degradation.18. The process of claim 15 wherein said dispersion ofhydrocarbon-containing sites are essentially free of halogen-containingsurfactant.
 19. The process of claim 18 wherein said dispersion ofpolymerization sites are free of halogen-containing surfactant.
 20. Theprocess of claim 15 wherein said dispersion of polymerization sites isessentially free of hydrocarbon-containing compound, includinghydrocarbon-containing surfactant.
 21. The process of claim 1 wherein nofluorosurfactant is present in said aqueous medium.
 22. The process ofclaim 1 wherein said fluoropolymer is fluoroplastic.
 23. The process ofclaim 1 wherein said fluoropolymer is perfluoroplastic.
 24. The processaccording to claim 1 wherein the dispersion of fluoropolymer particlescomprises no more than 50 ppm of fluorosurfactant.
 25. The process ofclaim 1 wherein said fluoropolymer is selected from the group consistingof polytetrafluoroethylene, modified polytetrafluoroethylene, andmelt-processible copolymer comprising at least 40-99 mol %tetrafluoroethylene units and about 1-60 mol % of at least one othermonomer.
 26. The process of claim 1 wherein said fluoropolymer is aperfluoroplastic selected from the group consisting ofpolytetrafluoroethylene, modified polytetrafluoroethylene andmelt-fabricable copolymers mentioned above comprising 60-98 wt %tetrafluoroethylene units and 2-40 wt % of at least one otherperfluoromonomer.